Servings: About 60 cookies

FOR THE VANILLA SHORTBREAD: subheading: FOR THE VANILLA SHORTBREAD:
1½ cups/192 grams all-purpose flour 1½ cups/192 grams all-purpose flour
½ teaspoon kosher salt (such as Diamond Crystal) ½ teaspoon kosher salt (such as Diamond Crystal)
½ cup/112 grams unsalted butter, at room temperature ½ cup/112 grams unsalted butter, at room temperature
½ cup/100 grams granulated sugar ½ cup/100 grams granulated sugar
1 large egg, yolk and white separated, at room temperature 1 large egg, yolk and white separated, at room temperature
2 teaspoons vanilla extract 2 teaspoons vanilla extract
FOR THE STRAWBERRY SHORTBREAD: subheading: FOR THE STRAWBERRY SHORTBREAD:
1 (1.2-ounce/34-gram) package freeze-dried strawberries (about 2 cups slices) 1 (1.2-ounce/34-gram) package freeze-dried strawberries (about 2 cups slices)
1¼ cups/160 grams all-purpose flour 1¼ cups/160 grams all-purpose flour
½ teaspoon kosher salt (such as Diamond Crystal) ½ teaspoon kosher salt (such as Diamond Crystal)
½ cup/112 grams unsalted butter, at room temperature ½ cup/112 grams unsalted butter, at room temperature
½ cup/100 grams granulated sugar ½ cup/100 grams granulated sugar
1 large egg, yolk and white separated, at room temperature 1 large egg, yolk and white separated, at room temperature
FOR THE CHOCOLATE SHORTBREAD: subheading: FOR THE CHOCOLATE SHORTBREAD:
1¼ cups/160 grams all-purpose flour 1¼ cups/160 grams all-purpose flour
¼ cup/23 grams cocoa powder ¼ cup/23 grams cocoa powder
½ teaspoon kosher salt (such as Diamond Crystal) ½ teaspoon kosher salt (such as Diamond Crystal)
½ cup/112 grams unsalted butter, at room temperature ½ cup/112 grams unsalted butter, at room temperature
½ cup/100 grams granulated sugar ½ cup/100 grams granulated sugar
1 large egg, yolk and white separated, at room temperature 1 large egg, yolk and white separated, at room temperature

Prepare the vanilla shortbread: Whisk together flour and salt in a medium bowl. In the bowl of a stand mixer fitted with a paddle, combine butter and sugar on medium speed until pale yellow, about 2 minutes, scraping down the sides a few times. Add the egg yolk (reserve egg white) and vanilla extract, and mix until combined, about 30 seconds. Scrape down the sides of the bowl, add the flour mixture all at once and mix on low until it all resembles coarse pea-size crumbs. Transfer to a piece of plastic wrap and scrape the bowl and paddle clean. (No need to wash.)
Prepare strawberry shortbread: Pulse freeze-dried strawberries in a food processor until powdered (some crumbs are fine). You should have about ⅔ cup ground strawberries. Transfer to a medium bowl. Add flour and salt, and whisk to combine.
Add butter and sugar to the stand mixer bowl, and mix together on medium speed until pale yellow, about 2 minutes, scraping down the sides a few times. Add the egg yolk (reserve egg white) and mix until combined, about 30 seconds. Scrape down the sides of the bowl, add the flour mixture and mix on low until it all resembles coarse pea-size crumbs. Transfer to a second piece of plastic wrap.
Prepare the chocolate shortbread: Whisk together flour, cocoa powder and salt in a medium bowl. Add butter and sugar to the stand mixer bowl and mix together on medium speed until pale yellow, about 2 minutes, scraping down the sides a few times. Add the egg yolk (reserve egg white) and mix until combined, about 30 seconds. Scrape down the sides of the bowl, add the flour mixture and mix on low until it all resembles coarse pea-size crumbs. Transfer to a third piece of plastic wrap and scrape the bowl and paddle clean. (No need to wash.)
With your hands, pat doughs into rough 5-by-10-inch rectangles and wrap them tightly in the plastic wrap. Using a rolling pin, roll the doughs so they are ½ inch tall. (If they’re larger than 5-by-10 inches, they can be trimmed to 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 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 strips to the fridge so they stay firm while you work.
To form the checkerboard pattern, lay a strip of each flavor on a cutting board (chocolate, strawberry, vanilla), 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 pressing. 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.

The cookies can be stored up to 1 week in an airtight container.  The cookies can be stored up to 1 week in an airtight container.
The assembled dough logs can be stored in the freezer for up to 3 months, then thawed in the refrigerator until ready to slice and bake.  The assembled dough logs can be stored in the freezer for up to 3 months, then thawed in the refrigerator until ready to slice and bake.