Neapolitan Checkerboard Cookies

Begin by preparing the vanilla shortbread. In a medium bowl, whisk together the flour and salt. In the bowl of a stand mixer fitted with a paddle attachment, combine the butter and sugar on medium speed until it turns pale yellow, which should take around 2 minutes. Be sure to scrape down the sides a few times. Add the egg yolk (set aside the egg white) and vanilla extract, and mix until well combined, roughly 30 seconds. Scrape down the sides of the bowl, add the entire flour mixture at once, and mix on low until the mixture resembles coarse crumbs about the size of peas. Transfer this mixture to a sheet of plastic wrap, and make sure to scrape the bowl and paddle clean. (There's no need to wash the mixer bowl.)

To make the strawberry shortbread, blend the freeze-dried strawberries in a food processor until they turn into a powder, leaving some small crumbs if desired. You should end up with around ⅔ cup of crushed strawberries. Next, transfer this strawberry mixture to a medium-sized bowl and mix it with the flour and salt, whisking them together until well combined.

Combine butter and sugar in the stand mixer bowl and beat them at medium speed until they turn pale yellow, which should take approximately 2 minutes. Remember to scrape down the sides of the bowl as needed. Next, add the egg yolk (keep the egg white aside) and mix until it's well incorporated, which should take around 30 seconds. Scrape down the sides of the bowl again, and then add the flour mixture, mixing on low until the mixture becomes coarse crumbs about the size of peas. Afterwards, transfer this mixture to a separate piece of plastic wrap.

To prepare the chocolate shortbread, combine the flour, cocoa powder, and salt in a medium-sized bowl, whisking them together. In the stand mixer bowl, add the butter and sugar once more. Mix at medium speed until the mixture lightens and becomes pale yellow, typically taking about 2 minutes. Be sure to scrape down the sides of the bowl as needed during this process. Add the egg yolk (remember to keep the egg white aside) and mix until thoroughly incorporated, which should take roughly 30 seconds. Once again, scrape down the sides of the bowl, then add the flour mixture and mix on low until it resembles coarse crumbs, similar in size to peas. Transfer this crumbly mixture to a third piece of plastic wrap, ensuring you scrape the bowl and paddle clean. (No need to wash the mixer bowl.)

Form the dough into approximately 5 by 10-inch rectangles with your hands and tightly wrap them in plastic wrap. Use a rolling pin to flatten the dough until it reaches a thickness of approximately ½ inch. If they end up larger than 5 by 10 inches, don't worry; you can trim them down to the correct size later.

To assemble, whisk the reserved egg whites with 1 tablespoon water to break up the whites. Trim any uneven edges from the dough (or if the dough is larger, trim down to 5-by-10-inch rectangles).

Cut each dough into 9 (½-inch-wide, 10-inch-long) pieces. Once sliced, transfer the strips to the fridge to stay firm while you work.

To form the checkerboard pattern, lay a strip of each flavor (chocolate, strawberry, vanilla) on a cutting board, brush with the egg white mixture, and gently press the long sides together so they adhere. Layer another 3 strips (strawberry, vanilla, chocolate), repeat with egg white, and press. Repeat with the last layer (vanilla, chocolate, strawberry). You should have a long 3-by-3 square. Repeat with the remaining dough strips until you have 3 logs. Wrap with plastic and transfer to the refrigerator to chill overnight.

When ready to bake, heat oven to 350 degrees. Line 2 baking sheets with parchment paper. Remove one log at a time and square up any uneven edges, then slice the dough crosswise into ⅓-inch-thick squares.

Space the squares about 1 inch apart on the baking sheets and bake until the edges are lightly golden, 12 to 13 minutes, rotating the pans halfway through. Allow the cookies to cool on the baking sheets for about 5 minutes and then transfer to a wire rack to cool completely.