Preheat the oven to 350°F. Line two baking sheets with parchment paper. Pour the granulated sugar into a small bowl. Pour the powdered sugar into a second small bowl. Set both aside.
In a stand mixer fitted with the paddle attachment, beat together the butter, brown sugar, and granulated sugar on low speed until combined. Gradually increase the speed to medium-high and mix until light and fluffy, about 2 minutes.
Use a silicone spatula to scrape down the sides and bottom of the bowl, then add in the eggs, vanilla and peppermint extract. Beat on medium-high speed until the mixture is smooth and fluffy, about 1 minute, scraping down the bowl as needed.
Add the flour, cocoa powder, baking powder, baking soda, and salt. Beat on low speed until just combined and no streaks of flour remain, about 30 seconds.
Use a 1 ½ ounce cookie scoop to portion out equal amounts of dough. Roll the dough in your hands to smooth the edges. Roll the dough balls in the granulated sugar first, then roll them in the powdered sugar, evenly coating the outside of the cookie. Place the cookies on the prepared baking sheets, spacing them 2 inches apart.
Bake until the cookies have formed cracks all over and are set and firm around the edges but still somewhat soft in the middle, 9 to 10 minutes. Allow the cookies to cool completely on the baking sheet before serving.