Line two baking sheets with parchment paper and set aside. **If you will be using cold butter, preheat oven to 350℉. **If you are using room temperature butter, wait until dough is chilling to preheat oven. **(see note)
Using a whisk or dough hook, combine dry ingredients including flour, cocoa powder, baking soda, baking powder and salt. Set aside.
Cream together the butter and both sugars using a stand mixer fitted with the paddle attachment or a hand mixer. Add eggs, vanilla extract and peppermint extract and mix again until just combined.
Add flour mixture into the wet ingredients and mix again until just combined. Do not overmix.
Mix chocolate chips and mint baking chips into the dough by hand using a wooden spoon or sturdy spatula.
Using a 2 ounce cookie scoop, place up to 8 (level to slightly overfull) scoops of dough on each prepared baking sheet, evenly spaced.
Chill scooped cookie dough on baking sheets in the fridge for 40 minutes. **If you used cold butter, skip this step. **(see note)
Preheat oven to 350℉. **(see note)
Bake for 14-16 minutes, until cookies are set. Halfway through baking time, rotate trays and baking racks in the oven (so that the tray that was on top is now on the lower rack and the part of the baking trays that was at the front of the oven is now at the back of the oven).
Transfer each cookie sheet to a wire rack. Enjoy warm or cool completely on trays.