01 - Whisk together flour, baking powder, and salt in a medium bowl. Set aside for later use.
02 - Beat butter and sugar in a large bowl until light and fluffy. Add egg and vanilla, mixing until fully combined.
03 - Gradually add flour mixture to wet ingredients, mixing just until dough forms. Be careful not to overmix.
04 - Divide dough into three equal portions. Mix one portion with cocoa powder for chocolate layer. Mix second portion with strawberry powder and optional food coloring. Leave third portion plain for vanilla layer.
05 - Roll each dough portion between parchment paper into equal rectangles (approximately 10x6 inches). Chill each sheet for 20-30 minutes until firm.
06 - Layer chocolate dough on bottom, vanilla in middle, and strawberry on top. Gently press layers together to ensure they adhere.
07 - Starting from the long edge, roll stacked dough tightly into a log. Wrap in plastic wrap and refrigerate for at least 1 hour until very firm.
08 - Preheat oven to 350°F. Line baking sheets with parchment paper.
09 - Slice chilled dough log into 1/4-inch rounds. Place cookies 2 inches apart on prepared baking sheets. Bake for 10-12 minutes until edges are lightly golden.
10 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely before storing.