01 - Whisk together flour, baking powder, and salt in a medium bowl until well combined. Set aside for later use.
02 - Beat softened butter and granulated sugar in a large bowl until the mixture becomes light and fluffy, approximately 3-4 minutes. Add the egg and vanilla extract, mixing until fully incorporated.
03 - Gradually add the prepared flour mixture to the wet ingredients, mixing on low speed just until a dough forms. Avoid overmixing to prevent tough cookies.
04 - Split the dough into three equal portions. Mix one portion with cocoa powder until thoroughly combined for the chocolate layer. Mix another portion with freeze-dried strawberry powder (and a drop of pink food coloring if using) until the color is uniform. Leave the third portion plain for the vanilla layer.
05 - 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 enough to handle.
06 - Carefully place the chocolate layer on the bottom, top with the vanilla layer, then finish with the strawberry layer. Gently press the layers together to ensure they adhere.
07 - Starting from one long edge, tightly roll the stacked dough into a uniform log. Wrap securely in plastic wrap and refrigerate for at least 1 hour until the log is very firm and easy to slice.
08 - Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
09 - Slice the chilled dough log into 1/4-inch thick rounds using a sharp knife. Place cookie slices 2 inches apart on the prepared baking sheets to allow for spreading.
10 - Bake for 10-12 minutes or until the edges are just lightly golden. The centers should remain slightly soft. Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.