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. Avoid overmixing.
04 - Split dough into three equal portions. Mix one portion with cocoa powder for chocolate layer. Mix second portion with strawberry powder and optional food coloring. Keep third portion plain for vanilla layer.
05 - Roll each portion between parchment paper into equal rectangles (approximately 10x6 inches). Chill sheets for 20-30 minutes until firm.
06 - Stack dough layers in order: chocolate on bottom, vanilla in middle, strawberry on top. Press layers together gently.
07 - Starting from the long edge, roll stacked dough tightly into a log. Wrap in plastic and chill for at least 1 hour until very firm.
08 - Preheat oven to 350°F. Line baking sheets with parchment paper.
09 - Cut chilled log into 1/4-inch rounds. Place cookies 2 inches apart on prepared sheets. Bake for 10-12 minutes until edges are lightly golden.
10 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool completely.