2sticks(226 grams) unsalted butter, at cool room temperature
3/4cup(150 grams) granulated sugar
1large egg, at cool room temperature
1/2teaspoonvanilla extract
1teaspoonpeppermint extract
1/2teaspoongreen food coloring
3tablespoons(16 grams) unsweetened cocoa powder
1tablespoonmilk
Instructions
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large bowl, use an electric mixer to beat the butter and sugar on medium-high speed until well-combined and smooth, about 2 minutes. Add the egg and extracts and beat until combined. On low speed, gradually add the flour mixture and beat until incorporated. Remove half the dough from the bowl and set aside. Beat green food coloring into one portion of dough until evenly colored. Into other half of dough, stir in cocoa powder and milk until just combined.
Place the chocolate dough between two large sheets of parchment paper. Roll dough into a large rectangle about 1/4-inch thick. Repeat with remaining green dough. Carefully place the green dough rectangle on top of the chocolate dough rectangle, peeling away the parchment from the green dough. Trim edges if necessary. Using the parchment paper under the chocolate dough as a guide to prevent sticking, roll the long side of the dough into a tight log, creating a pinwheel effect. Wrap log in plastic wrap and freeze for 30 minutes, or until firm.
Meanwhile, preheat oven to 350°F. Line large baking sheets with parchment paper.
Using a sharp knife, slice the dough log into 1/2-inch slices. Place slices on prepared baking sheets, spacing 2 inches apart. Bake for 10 to 12 minutes, or until set. Remove baking sheets to the cooling racks and let cool for 2 minutes before removing the cookies to wire racks to cool completely.
Cookies can be stored in an airtight container at room temperature for up to 5 days or in the freezer for up to 1 month.