Heat oven to 350°.
Spray cookie sheets with cooking spray.
In large mixing bowl, mix softened butter, sugars, baking soda, salt, eggs, vanilla, and cocoa.
Add UNBLEACHED flour (bleached flour toughens cookies), and mint chocolate chips.
Stir in with a wooden spoon.
Do not use an electric mixer or cookies will be tough.
Roll into balls and place on sprayed cookie sheets.
Bake at 350° for 10-12 minutes or until set. (Mine took 14 minutes).
Cool 1 minute; remove from cookie sheets cool completely.