Whisk together the flour, baking powder, and salt in a medium bowl.
Beat the butter and sugar in a large bowl for 2–3 minutes until creamy.
Add the egg and vanilla extract and mix until combined.
Gradually add the dry ingredients and mix just until a soft dough forms.
Divide the dough into two equal portions. Color one red and the other green using gel food coloring.
Roll each portion between parchment paper into a rectangle about ¼ inch thick.
Place the green rectangle over the red rectangle, trim the edges if needed, and roll tightly from one long side into a log.
Wrap the log in plastic wrap and refrigerate for at least 2 hours, until firm.
Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.
Slice the dough log into rounds about ¼ inch thick and place them about 2 inches apart on the baking sheets.
Bake for 10–12 minutes, until the edges are set and the bottoms are lightly golden.
Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.