Step 1: Make the Dough

In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the egg and vanilla extract until smooth.

In a separate bowl, whisk together flour, baking powder, and salt. Gradually mix the dry ingredients into the wet mixture until a soft dough forms.

Step 2: Divide and Color

Split the dough evenly into two portions. Tint one half red and the other green using gel food coloring. Mix each until the color is evenly distributed.

Step 3: Roll and Layer

Roll each colored dough between two sheets of parchment paper into rectangles about ¼ inch thick. Stack one layer over the other, brushing a little water between them to help them stick.

Starting from a long edge, roll tightly into a log to form your swirl.

Step 4: Chill the Dough

Wrap the dough log in plastic wrap and refrigerate for 1–2 hours (or overnight). Chilling keeps your swirls crisp when slicing.

Step 5: Slice and Bake

Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.

Slice chilled dough into ¼-inch rounds and place 1 inch apart on the baking sheet.

Bake for 8–10 minutes, until the edges are just set but not browned.

Step 6: Cool and Decorate

Cool cookies on a wire rack. For extra flair, drizzle with melted white chocolate or roll edges in sprinkles before baking.