Preheat the oven to 350℉. Line baking sheet(s) with parchment paper or silicone baking mat(s).

In a large bowl, using an electric handheld mixer, beat the softened butter, sugar, and brown sugar for 30 seconds, starting on low speed and increasing to high speed as the mixture comes together. Add the egg, egg yolk, and vanilla and peppermint extracts and beat on high speed until fluffy.

Whisk together the flour, cocoa powder, and baking soda. Add the butter mixture and mix on low speed just until incorporated. Fold in the chopped chocolate mints.

Roll dough into balls (using about 1 tablespoon of dough per cookie). Roll each cookie dough ball in the icing sugar to coat before placing it on the lined baking sheet(s), leaving 2 inches between each cookie for spreading room.

Bake cookies, one pan at a time, for 9-11 minutes or until the tops start to crack. Let the cookies cool on the pan for 5 minutes and then transfer to a wire rack to finish cooling. Finish baking the remaining cookies. Enjoy!