Combine flour, baking powder, salt, and cocoa powder in a bowl. Whisk together, and set aside.
With a mixer, cream the butter and sugars together until light and fluffy — at least 3-5 minutes. Add the eggs, one at a time, scraping down sides of the mixing bowl as needed. Add the vanilla extract.
The dough will be very firm, so gently fold in the mint chips.
Chill the dough for 30 minutes.
Preheat the oven to 350 F. Using a small cookie scoop, or a spoon, form ⅛ cup balls of dough. Flatten slightly.
The cookies will not spread very much during baking, so set them 1 to 2 inches apart on a lined cookie sheet. Cook for 9-11 minutes. They will not look done, but the edges will be set.
Remove from the oven and let cool for a few minutes on the cookie sheet before moving to a cooling rack.
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/chocolate-mint-chip-cookies/