In a stand mixer with the paddle attachment, beat butter, sugar, eggs, & vanilla until light & fluffy.
Combine flour, cocoa, baking soda & salt in a separate bowl. Gradually add to wet mixture until combined.
Fold in mint chips.
Spoon cookie dough onto parchment lined baking sheets. Bake at 350?F for 8-10 minutes (they will look underdone, but will finish baking on the pan as they cool.)