1. In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 2–3 minutes.

2. Beat in the egg and vanilla extract until well combined.

3. In a separate bowl, whisk together the flour, baking powder, and salt.

4. Gradually add the dry ingredients to the wet mixture, mixing on low speed just until combined.

5. Divide the dough evenly into two portions.

6. Tint one half of the dough with red gel food coloring and the other half with green, mixing each until the color is fully incorporated.

7. Form each colored dough into a flat disk, wrap in plastic wrap, and refrigerate for at least 1 hour.

8. On a lightly floured surface, roll out the red dough into a 12×9-inch rectangle. Repeat with the green dough.

9. Carefully place one rectangle on top of the other and gently press together.

10. Starting from the long edge, tightly roll the stacked dough into a log, creating a spiral pattern.

11. Wrap the log in plastic wrap and refrigerate for at least 4 hours or overnight. For clean slicing, freeze for 30–60 minutes before cutting.

12. Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.

13. Slice the chilled dough log into ¼-inch rounds.

14. Place cookies 2 inches apart on the prepared baking sheets.

15. Bake for 10–12 minutes or until the edges are just barely golden.

16. Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.