1. Preheat oven to 375°F. In the bowl of a mini food processor, combine mint and sugar. Process until mint is finely chopped. Set aside. In a small bowl, whisk together flour, baking soda and salt.
2. In a standup mixer bowl fitted with the paddle attachment, beat butter, mint sugar, brown sugar and vanilla extract until creamy. Add eggs, one at a time, beating well after each addition. Gradually beat in flour mixture. Stir in chocolate pieces.
3. Drop by two to three tablespoon-sized balls onto ungreased baking sheets. Bake for nine to 11 minutes or until golden brown. Cool on baking sheets for 2 minutes, and then transfer to wire racks to cool completely.