Heat oven to 350 F

Beat butter and sugar, on medium speed until creamy

Add egg and vanilla, beat well

Stir together flour, cocoa, baking soda and salt

Gradually add dry mixture to butter mixture, beating well

Stir in mint chocolate chips

Drop by rounded teaspoons onto ungreased baking sheet

Bake 8-9 minutes or just until set - do not overtake

Cool slightly on pan

Remove to wire rack and cool completely