01 - In a medium bowl, whisk together flour, baking powder, and salt until well combined. Set aside for later use.
02 - In a large bowl, beat softened butter and granulated sugar together using an electric mixer until the mixture becomes light and fluffy, approximately 3-4 minutes.
03 - Add the egg and vanilla extract to the butter mixture. Continue mixing until fully incorporated and smooth.
04 - Gradually add the flour mixture to the wet ingredients, mixing on low speed just until a dough forms. Be careful not to overmix.
05 - Divide the dough into three equal portions, weighing approximately 6-7 ounces each for uniform layers.
06 - Knead cocoa powder into one dough portion until the color is evenly distributed throughout.
07 - Mix freeze-dried strawberry powder (and pink food coloring if using) into another dough portion until color is consistent.
08 - Keep the remaining dough portion plain as the vanilla layer.
09 - Roll each dough portion between two sheets of parchment paper into rectangles measuring approximately 10x6 inches. Chill each sheet for 20-30 minutes until firm.
10 - Carefully place the chocolate layer on the bottom, top with the vanilla layer, then finish with the strawberry layer. Gently press layers together to ensure they adhere.
11 - Starting from the long edge, tightly roll the stacked dough into a log. Wrap completely in plastic wrap and refrigerate for at least 1 hour until very firm.
12 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
13 - Slice the chilled dough log into 1/4-inch thick rounds using a sharp knife. Place cookies 2 inches apart on prepared baking sheets.
14 - Bake for 10-12 minutes or until edges are just lightly golden. Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.