FOR BROWNIES: Preheat oven to 350° F. Line two baking sheets with parchment paper or spray with non-stick spray.
In a large microwave-safe bowl, add the chopped chocolate and butter. Microwave, at 30 second intervals, until chocolate is melted. Stir to combine. Set aside and let mixture cool 10 minutes.
In a separate bowl, add eggs, sugar and vanilla. Whisk mixture together to combine. Pour the cooled chocolate into the egg mixture and stir to combine. Fold in the flour and baking powder. Stir in chocolate chips. Cover bowl with saran wrap and chill in fridge for 30 minutes.
Once chilled, scoop 2 Tablespoons of dough onto prepared baking sheets. Bake cookies for 10-12 minutes. Do not over bake! Leave to cool on the baking sheets.
FOR FROSTING: Using an electric-mixer, beat the powdered sugar and butter until combined. Slowly add in cream or milk, until frosting reaches your desired consistency. Add the peppermint extract and green food coloring; mix until thoroughly combined. Frost cooled cookies with frosting. Sprinkle tops with extra chocolate chips, if desired.