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

Cream together 1 cup of softened unsalted butter and 1 ½ cups of granulated sugar until light and fluffy (3-5 minutes).

Add 1 large egg and 1 teaspoon of vanilla extract; mix until fully incorporated.

Whisk together 2 ½ cups of all-purpose flour, 1 teaspoon of baking powder, and ¼ teaspoon of salt in a separate bowl, then combine with the butter mixture.

Divide the dough into two portions. Mix ⅓ cup of unsweetened cocoa powder into one portion to create the chocolate dough.

Roll out the plain dough and chocolate dough between parchment paper into ¼ inch thick rectangles.

Layer the chocolate dough over the plain dough and roll up tightly to form a log.

Wrap the dough log in plastic wrap and refrigerate for at least 30 minutes.

Slice the chilled log into ¼ inch thick rounds and place on baking sheets.

Sprinkle the tops with red and green sprinkles or crushed peppermint candies if desired.

Bake for 10-12 minutes until edges are lightly golden.

Cool on the baking sheet for a few minutes before transferring to a wire rack.