Preheat oven to 350 degrees. Prepare baking sheets with parchment paper or silicone baking mats.
Cream the butter and sugar together. Add the extracts and eggs and beat well.
In a separate bowl mix the cocoa powder with the flour, cornstarch, baking soda, baking powder and salt.
Add the dry ingredients to the butter mixture and mix well. Add the chocolate chips and mix until combined.
Scoop rounded tablespoonfuls 2" apart onto the prepared baking sheets. Place baking sheets in the fridge and chill 45 minutes - 1 hour until the dough is completely chilled.
Place chilled dough in the oven and bake for 9-11 minutes or until the bottoms look slightly darker. Remove from the oven and let cool 10 minutes on the baking sheet before transferring to a baking sheet to cool completely.
I used semisweet mint chocolate chips, but feel free to sub in all semisweet chips of a mix of semisweet chocolate chips and mint chips or whatever you'd like!