In a large bowl, mix the flour, cocoa powder, baking soda, and salt. Set aside.
In the base of a stand mixer with a paddle attachment (or with a hand mixer), cream the butter, granulated sugar, and brown sugar on medium-high speed until light and fluffy (about 2-3 minutes).
Add the egg, peppermint extract, and vanilla extract to the butter mixture. Beat on medium-high speed until combined.
On low speed, gradually add the dry ingredients to the wet mixture in three parts, mixing until just combined. Stir in the mini chocolate chips.
Cover the dough and refrigerate for at least 2 hours.
Preheat the oven to 350°F and line a baking sheet with parchment paper. Remove the dough from the fridge and let it sit for 15 minutes.
Scoop the dough into balls (about 1.5 tablespoons each). Roll each ball first in granulated sugar, then generously coat in confectioners' sugar. Place the dough balls 3 inches apart on the baking sheet.
Bake for 11 minutes. If the cookies aren’t spreading, remove them from the oven a few minutes before they are done and lightly bang the baking sheet on the counter to help them spread.
Let the cookies cool and enjoy! These cookies are also delicious when frozen.