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 incorporated.
03 - Gradually add flour mixture to wet ingredients, mixing just until dough forms. Be careful not to overmix.
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. Leave third portion plain for vanilla.
05 - Roll each portion between parchment paper into 10x6 inch rectangles. Chill sheets for 20-30 minutes until firm.
06 - Layer dough sheets in order: chocolate on bottom, vanilla in middle, strawberry on top. Press gently to adhere layers.
07 - Roll stacked dough tightly from long edge into a log. Wrap in plastic and refrigerate 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 baking sheets.
10 - Bake for 10-12 minutes until edges are lightly golden. Cool on baking sheet for 5 minutes, then transfer to wire rack to cool completely.