Preheat your oven to 350°F (175°C).
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large bowl, cream the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add the egg, vanilla extract, and peppermint extract, then mix until well combined.
Gradually add the dry flour mixture to the wet ingredients, mixing just until incorporated.
Divide the dough into two equal portions; color one portion with red food coloring and the other with green.
Take a spoonful of each color and layer them together, then gently twist to create a swirl effect.
Roll the dough into logs about 1 inch in diameter and wrap them in plastic wrap. Chill in the refrigerator for at least 30 minutes.
Slice the chilled logs into ¼-inch thick rounds and place them on a baking sheet lined with parchment paper.
Sprinkle the tops with crushed peppermint candies before baking.
Bake for 10-12 minutes, or until the edges are lightly golden.
Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.