Preheat over to 350°.
Sift flour and cocoa, then combine with baking soda and salt. Set aside.
In a large bowl, beat butter, granulated sugar, brown sugar and vanilla until creamy. Add eggs, one at a time, beating well after each egg. Gradually add flour mixture. Stir in mint chips. Drop by rounded teaspoonfuls onto ungreased cookie sheets.
Bake 8 minutes. Do not overbake.
TIP: Can't find mint chocolate chips? Try making your own. Pour 1 (12-ounce) bag of chocolate chips into a 1-gallon resealable storage bag, then place the bag flat on a cookie sheet. Pour 2 teaspoons of peppermint extract in a small dish, then place it inside the bag with the chips, being careful not to spill. Seal bag and let sit overnight to allow chips to absorb the flavoring.