In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the egg and vanilla extract, mixing until fully combined.

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

Divide the dough evenly into two portions. To one portion, mix in cocoa powder until fully incorporated. If the dough feels slightly dry, add a tablespoon of milk.

To the second portion, mix in peppermint extract and optional red food coloring.

Wrap both dough portions in plastic wrap and refrigerate for at least 1 hour. Chilling makes rolling and shaping much easier.

Roll out each dough portion into a rectangle of similar size on lightly floured parchment paper. Carefully place one layer on top of the other.

Gently press together and roll the stacked dough into a tight log, starting from the longer edge to create a swirl pattern.

Wrap the log and chill for another 20–30 minutes to firm up.

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

Slice the chilled dough log into ½-inch rounds and place on the baking sheet, spacing slightly apart.

Bake for 10–12 minutes, or until edges are set but centers remain soft. Do not overbake.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack.

If desired, drizzle with melted chocolate or sprinkle with crushed peppermint candies while still slightly warm.