In the bowl of a stand mixer fitted with the whisk attachment, beat the butter, powdered sugar, and sugar together on high speed for 1 minute.
1 cup unsalted butter, ¼ cup powdered sugar, ¼ cup granulated sugar
Add the flour, peppermint extract, and salt and beat together until smooth.
2 cups all-purpose flour, ¾ teaspoon peppermint extract, ½ teaspoon kosher salt
Divide the dough into 2 equal sections. Keep one section in the stand mixer bowl and place the other section in a separate bowl.
Add a drop or 2 of red food coloring to the dough that is still in the stand mixer bowl. Beat together until all of the dough is red.
Red food coloring
Place a large piece of plastic wrap onto the counter. Place the white (no food coloring added) dough on top. Use a rolling pin to roll the dough into a rectangle (approximately 7x9 inches).
Remove the red dough from the bowl and carefully press or roll it out on top of the white dough. It should completely cover the white dough (and become the same shape as the white dough).
Before rolling, slice about ¼ inch of dough off of the end closest to you so there’s a nice, neat line of dough to start with. This ensures pretty pinwheel centers.
Use the plastic wrap the help you roll the dough into a log. Do not wrap the plastic wrap into the log. Once the dough is in a tight log, tightly wrap with plastic wrap and place in the refrigerator to chill for at least 1 hour.
Once the dough log has chilled, preheat oven to 350°F. Line a baking sheet with parchment paper.
Remove the dough from the refrigerator, unwrap, and place on a cutting board. Cut the log into cookies about ½-inch thick.
Place the cookies onto the prepared baking sheet leaving 2 inches of space between them.
Bake cookies for 10 minutes - the cookies will still look soft at this point.
Remove them from the oven and place on a cooling rack to cool before serving.