To create the custom shapes, I 3D printed molds. To create the molds, I first drew a set of 43 mm by 53 mm designs—the size I measured the commercially-available cookies to be—in Inkscape, making each line at least 2 mm thick, to ensure it would survive the molding and baking process. In the end, I settled on twelve designs: four designs showing E- and B-mode polarization patterns; four designs with Antarctica themes, specifically, an Adélie penguin, the True South flag, an Antarctica outline, and the ceremonial Pole marker; and four designs with BICEP themes, specifically, the Dark Sector Laboratory (DSL) building with BICEP3 ground shield, the BICEP3 cryostat, the BICEP Array tower connected to the Martin A. Pomerantz Observatory (MAPO) building, and a BICEP Array cryostat. After converting the outlines of the designs to paths and taking their union, each design was individually exported in the DXF R14 format and converted into solid models using a custom CadQuery script. The molds were then printed out of PLA using a Prusa MINI+ 3D printer using 0.1 mm layer height. For initial prototypes, the molds were designed to act as both molds and cookie cutters, but the dough would get stuck in the mold. Instead, the design was modified to only cut out the corners, leaving the sides connected to the rest of the rolled out dough; after removing the molds, the sides were cut with a dull knife, freeing the cookies from the dough.

Others have previously baked cookies in this style, so I had an existing reference for a recipe to use. However, I tried to more closely follow Pepperidge Farm’s recipe based on the ingredients list and nutritional information. In the end, I settled on a recipe of 3/4 cup butter, 3/4 cup granulated sugar, 1 3/4 cup all-purpose flour, and 1/2 cup corn starch. Originally, I had included 1 teaspoon of baking powder—as a substitute for the baking soda and cream of tartar in the commercially-available cookies—and less flour and corn starch to better match the fat–sugar–carbohydrate ratio in the nutritional information, but the cookies rose and spread too much during baking, ruining the designs. Thus, I removed the leavening agent and increased the amounts of flour and corn starch to the values listed above. As eggs are listed as being less than 2% of the cookies, I suspect they are only used for the wash, so I left them out of my dough recipe.¹

To make the dough, I partially melted the butter and mixed it with the sugar using a fork. Separately, I mixed the flour and corn starch and then mixed it into the butter–sugar mix, first mixing in half the dry mix and then the rest, until the dough was well mixed. Next, I split the dough in half, wrapped it in plastic wrap, and chilled it. If the dough is too warm, it will stick to the molds, and if it is too cool, it is difficult to roll out, so a happy medium needs to be found. I rolled out the chilled dough between two layers of plastic wrap, to prevent it from sticking, to a thickness of 6 mm, using a rolling pin with disks on the ends that allow setting the thickness. Removing the top layer of plastic wrap, I then dusted flour onto the dough to reduce the risk of it sticking to the molds and used the molds to shape the cookies, pressing down on the molds using much of my body weight.

The mold is then carefully wiggled back and forth to free it from the dough without damaging the design. Originally, I had molded one cookie at a time (as is shown above), but I found that it’s better to press in all of the molds before removing any of them, since this prevents shifting of the dough from later molds from disturbing earlier cookie designs.²

Once the molds are removed, the cookies can be freed from the dough using a knife with a rounded, non-serrated end. Using the same knife (or some sort of small spatula), the cookies are then transferred to parchment paper and placed in a freezer. The remaining dough should be balled back up and placed in a refrigerator; the other half of the dough is then removed from the refrigerator, and the process is repeated. I found that this recipe and mold combination produces around 28 cookies in total.

After freezing the cookies for a least an hour, an egg yolk wash should be applied.³ To do this, I whisked an egg yolk using a fork and then carefully painted it on to just the raised design on the cookies using a foam brush (a suggestion from the recipe I had consulted). The cookies should then be returned to the freezer for at least another 15 minutes, such that they’re frozen when placed in the oven.

Finally, the cookies can be baked. I found this to be a finicky process, since the designs on the cookies would be damaged if the dough rose in the center of the cookies, but the bottom center of the cookies would be under-baked if the cookies were taken out of the oven too soon. In the end, I settled on a procedure using an oven preheated to 425°F, to try to quickly bake in the designs. Start by placing the frozen cookies and parchment paper on a room-temperature baking sheet and baking for 6 minutes; any more than this, and the center of the cookies would begin to rise, damaging the designs. Remove the baking sheet from the oven and allow the sheet and cookies to cool, without removing the cookies. Once the cookies have cooled to near room temperature, return them to the oven for an additional 3 minutes. Again allow them to cool on the baking sheet. Flip the cookies over, return them to the oven for a final 3 minutes, and then allow them to cool. The initial two runs in the oven bake in the designs, while the final oven run finishes baking the bottom of the cookies.

Overall, I was mostly happy with how the cookies came out. The taste and texture were nice, and the designs remained intact, although I would have preferred if the egg yolk wash on the designs made them darker. After dialing in the recipe and baking procedure with two prototype batches, I baked an additional two final batches, producing 60 “good” cookies,⁴ comprised of five of each of the dozen designs.⁵ Between molding the cookies and painting on the wash, it takes over an hour for a batch, and the entire process takes several hours once the cooling time and baking time are included.

My colleagues seem to have enjoyed the cookies.⁶ For anyone wanting to make similar cookies, I’ve uploaded the designs and the script used to create the molds.

1. It would also make it easier to make a vegan version of the recipe. I originally planned to make a vegan and gluten free version for colleagues with dietary restrictions, but I ran out of time.  ↩

2. It also allows the designs to be placed closer together, since the risk of disturbing the adjacent designs is significantly reduced.  ↩

3. If the dough is too warm, applying the wash can damage the designs on the cookies.  ↩

4. I also used some leftover dough from the earlier batches.  ↩

5. Except, I accidentally made one too few of the True South design.  ↩

6. There were several approving comments about how I had gone through the effort of producing both directions of B-mode patterns.  ↩

To make the crust, I followed an existing gluten-free, vegan recipe, which contains almond flour, rice flour, corn starch, sugar, and water, although I also added some cinnamon. This was baked for half an hour at 350°F and was the only part of the pie that was baked.²

Next came the blackberry filling. In order to use a plastic insert to form the shape of the galaxy, I couldn’t bake the pie with the filling, so I developed my own no-bake recipe for the filling. This consisted of combining 3 cups (thawed) frozen blackberries, 1 cup (thawed) frozen blueberries, 3 tablespoons sugar, 2 tablespoons corn starch, and 1 teaspoon lemon juice in a sauce pan and cooking it on the stove on low-to-medium heat while stirring continuously until the mixture started to bubble. The blueberries were added in addition to the blackberries to move the color balance away from the more reddish blackberries. After being thoroughly washed with soap and water, the insert was placed in the center of the pre-baked pie crust, and the hot blackberry filling was spooned in around it. The pie was then placed in the freezer overnight to solidify the filling.

The next day, the frozen pie was removed from the freezer, and the plastic insert was carefully extracted using pliers to grip the insert. This was done by pulling up on the insert from side to side, a little at a time, while pressing down on the adjacent frozen pie filling with a finger until the insert was removed.³ Once the insert was removed, the pie was return to the freezer to ensure it was thoroughly frozen for the next step.

To prepare the white filling for the galaxy, a recipe based on maja blanca was used.⁴ Best I can tell, such desserts are generally prepared using just corn starch as a thickener, but my initial test batches had a gelatin-like texture and consistency, which I didn’t like. I solved this by substituting rice flour for some of the corn starch, which results in a significantly different texture.⁵ For the final recipe, I combined 1 cup coconut milk, 3 tablespoons sugar, 2 tablespoons rice flour, 2 tablespoons corn starch, and ~1/8 teaspoon vanilla extract in a small saucepan and heated it on the stove over low-to-medium heat while stirring continuously until it thickened.⁶ I then carefully spooned the custard into the void in the pie, until it was filled.⁷

My original plan for the pie also included a few stars with diffraction spikes, either for HST or JWST, made out of holographic white chocolate. Unfortunately, with the combination of the chocolate and diffraction grating I was using, the holographic patterning only lasted a few seconds after removing the chocolate before disappearing. Furthermore, I was unable to remove the chocolate from the 3D-printed PLA plastic molds I was using. A backup idea of sifting on powdered sugar also didn’t work, as the sugar dissolved and disappeared after a few minutes. Even without the extra embellishments, the pie was still good enough to win second place in the baking contest.

I’ve uploaded the design files for the 3D-printed galaxy insert.

Edit (2023-05-13): The holographic chocolate didn’t work (at least in part) because the chocolate wasn’t tempered.

1. Although it ended up being a more general baking contest, the original email about the contest described it as a pie-baking contest, hence the pie.  ↩

2. I apologize in advance for the archaic units.  ↩

3. In retrospect, adding a draft angle to the insert would have been a good idea.  ↩

4. But without any corn.  ↩

5. I also tried using only rice flour, but this, unsurprisingly, produce a texture similar to that of cooked white rice, which couldn’t easily be spooned into the galaxy void in the blackberry filling.  ↩

6. The consistency change is significant and rapid, so it’s obvious when this happens.  ↩

7. A combination of a very small spoon and my fingers ended up working reasonably well.  ↩

In order to make the cookies, I designed and 3D printed a custom cookie cutter and a stencil for marking the individual mirror segments.

Following a recipe found online, I made gingerbread cookie dough, rolled it out between layers of plastic wrap, and began cutting out cookies.

After cooling the dough in the freezer to make it stiffer and easier to handle, the cookies were removed from the plastic wrap, transferred to a sheet pan lined with parchment paper, and baked.

As cookie dough is not dimensionally stable when baking, I used the cookie cutter on the cookies again immediately after removing them from the oven to make a more precise shape, a technique that has heritage from the Sierpiński carpet Linzer cookie I previously created.

The final step is to mark the 18 individual mirror segments. As with science and instrumentation, developing a suitable technique involved some experimentation. My original idea was to use the 3D-printed stencil to directly apply yellow glaze to the cookies, but this failed spectacularly, looking like blobs of yellow mustard that were not remotely hexagonal. Next, I 3D printed a razor-blade guide, made a thin sheet of glaze on a plate, and tried using a razor blade in combination with the guide to cut the sheet of glaze into appropriately-sized hexagons. This again was a disaster, since while I could cut the glaze just fine, it just crumbled when I tried to remove it from the surface it was on. I then switched from using glaze to using a cream-cheese frosting, 3D printed a hexagonal tube, and filled it with the frosting. I also filled the original stencil with frosting and placed both the frosting-filled stencil and frosting-filled tube in the freezer. The plan was to extrude the frozen frosting from the tube with a 3D-printed plunger and then cut it into thin hexagonal sheets with a razor blade. Unfortunately, my residential freezer is not cold enough, and the frosting did not freeze hard enough; I was unable to cut the frosting without deforming it, and the frosting did not come out of the stencil cleanly either.

Finally, I decided to just place the stencil on top of a cookie and sift powdered sugar over the stencil; the top surface of the cookie was first dipped in water to wet it to make the sugar stick better. This worked well, but the hexagonal segments did not match the color of the JWST mirror, being white instead of gold. While trying to find prior art for dissolving sugar in grain alcohol and aerosolizing the solution, I discovered that edible spray paint exists. It even comes in a metallic gold color! After securing the stencil on top of the cookie to prevent it from moving when sprayed, I applied three coats of gold color, allowing the spray to dry between coats.

This worked pretty well, although I discovered that spraying the bottom of the cookies worked better than spraying the top because the bottom had a darker color that provided more contrast with the gold and because the bottom was more planar, resulting in less overspray underneath the stencil.

In case you want to make your own cookies, the cookie cutter and stencil model files are available. Also included is the model file for the six-pointed star shown in the cookie photos.²

1. The launch is scheduled for Christmas Day, as of writing.  ↩

2. As JWST has three supports holding its secondary mirror, bright point sources in its images will have six diffraction spikes, differing from the four in Hubble Space Telescope images.  ↩

In order to create the 15 cm square cookie, I designed and 3D printed a set of cookie cutters out of PLA plastic.¹ These consisted of a wavy-edged square for the border of all the layers, a smaller square for the center of the three fractal layers, an even smaller square for second fractal iteration layer, and the smaller square with eight tiny squares around it for the final iteration layer. This set of cutters was a compromise between having a separate, complete cutter for each layer—which would have required more print time and material—and only making one cutter per size of cutout—which would be more difficult to align and use.

An existing Linzer cookie recipe was used for creating the cookie.² After preparing the dough and using the cookie cutters, the cut dough was placed in the freezer for a few minutes to cool to make it easier to transfer the large cookie layers to the baking sheet. The cookie layers were then baked. Since dough expands when baked—and baking is not great for maintaining dimensional tolerances in general—the cookie cutters were used again on the cookie layers’ internal cutouts as soon as the layers were removed from the oven. The baked cookie layers were then placed in the freezer and frozen to make them more durable and easier to handle.³ Once frozen, the layers were removed, and the edges of the cutouts were cleaned up with a knife and, in the case of the tiny squares on the final layer, a paperclip. The final layer was then dusted with powdered sugar, and the layers were assembled into the final cookie using raspberry jelly between the layers.

For a different take on Sierpiński carpet cookies, see Evil Mad Scientist Laboratories’ 2008 blog post on the subject.

1. I have uploaded the cookie cutter designs. ↩

2. The recipe is for 20 three-inch cookies, which was just enough for one, large Sierpiński carpet cookie.  ↩

3. I still managed to crack the final layer in half, but the damage is not particularly noticeable under the powdered sugar.  ↩

I saw two ways to make a cake shaped as a Hilbert curve, using an appropriately shaped baking mold or painstakingly carving the appropriate shape out of a baked cake, with the former option being the logical path to pursue. This raised the question, how does one create such a mold? Baking molds are generally either metal or silicone, with silicone having the distinct advantage of being much easier to work with for such a shape, since it can be cast at room temperature. Thus, one needs to create a mold with which to cast the silicone baking mold. Fortunately, 3D-printing is well suited for this, and I already had experience 3D-printing Hilbert curve geometries.

Starting from my existing Hilbert Curve solid models, I designed a two-part mold for a third-order geometric approximation of the Hilbert Curve. Compared to a single-part mold, a two-part mold allows for a thinner silicone wall thickness, which reduces silicone material usage and makes it easier to turn the mold inside-out, a necessary step in removing the eventual cake from the baking mold. This mold was printed from PETG—for no particular reason besides having it around—on a Lulzbot TAZ 6 printer; as the mold is rather large, a printer with a large build volume is necessary. A 1.2 mm nozzle was used to reduce the printing time, a single wall extrusion² and 10% infill were used to reduce material usage, and a raft was printed below the part to aid with removal from the printer’s bed. When generating the G-code, a solid layer was added just below the Hilbert curve geometry to ensure that it would print correctly with the low infill percentage.

Once the mold was assembled, 1 kg of food-safe silicone³ was mixed, vacuum degassed, poured into the mold, and allowed to cure.

While I had hoped that the two-part plastic mold would allow the silicone mold to be easily removed once it had cured, this was an incredibly naive notion. After all attempts to carefully disassemble the plastic mold and remove the cured silicone failed, I ended up smashing the plastic mold to bits in order to free the silicone mold.⁴

I then thoroughly washed the silicone mold and was finally ready to begin baking. To increase my chances of success, I decided to use a recipe meant for a Bundt pan, a lemon pound cake.⁵ The recipe is below, courtesy of my mother.

2.5 cups sugar
1 cup butter
4 eggs
1 teaspoon vanilla extract
0.5 teaspoon lemon extract
1 cup milk
1 tablespoon lemon juice
3 cups flour
0.5 teaspoon baking soda

In mixing bowl, cream together sugar and butter until light and fluffy. Add eggs one at a time, beating well after each. Stir in vanilla and lemon extracts. Mix lemon juice into milk. Thoroughly sift together the flour and baking soda. Add flour mixture to creamed mixture alternately with milk solution, beating well after each addition. Pour into greased mold.

The silicone baking mold was placed into an 8″ square cake pan for support⁶ and thoroughly greased with shortening; while silicone baking molds don’t need to be greased, in theory, I decided it was best to do so if I were to have any chance of removing the complicated cake geometry from the mold in one piece.

The cake was then baked at 350°F for 135 minutes, with a pan of water also in the oven to try to prevent the top crust from hardening too much. As the mold does not have a hole in the center like a Bundt pan does, this baking time is considerably longer than what was specified by the original recipe. I learned this the hard way, since my first attempt came out under-baked, ruining the curve geometry. Once removed from the oven, I allowed the cake to cool for half an hour, before placing it in the freezer for seven hours; I reasoned that a frozen cake would be the least likely to break apart while attempting to remove it from the mold. Once I removed the frozen cake from the freezer, I was able to flip it over and slowly and carefully turn the silicone mold inside-out to remove the cake in one piece, starting from the corners where the curve does not end.⁷

I then flipped the cake back over and sliced the bottom flat.

Finally, the cake was ready for its finishing touch, a lemon glaze, mixed from a ratio of one cup confectioner’s sugar to two tablespoons lemon juice. I carefully and methodically brushed on four coats of glaze using a silicone basting brush, completing the cake.

Sadly, I didn’t win anything, just like last time, but there was stiff competition from many excellent cakes. The model files from the mold are available.

1. H. Sagan, Space-Filling Curves (Springer-Verlag, 1994). ISBN: 9780387942650. DOI: 10.1007/978-1-4612-0871-6. ↩

2. This led to some gaps in the part’s wall, which allowed some silicone to leak into the interior of the mold, making removal more difficult. ↩

3. Smooth-On Smooth-Sil 940 ↩

4. The single wall extrusion helped here, as did the single bottom layer. ↩

5. I also like the taste. ↩

6. By happenstance, it fit almost perfectly; I had sized the mold based on silicone and available print volumes. ↩

7. One of the ends of the curve did break off partially, but it was easy to reattach. ↩