Mix & bake brownies according to directions on the box. Allow to cool completely.

To make mint icing: Place butter into a medium sized bowl. With a hand mixer, cream butter until fluffy. Add powdered sugar, milk, mint extract and a little bit of green food coloring (a little goes a long way and you don't want a green mouth.) Mix until smooth. Spread over cooled brownies.

For the chocolate icing: Microwave chocolate chips, milk, butter, and vanilla in a medium sized microwave-safe bowl for 30 to 40 seconds. Whisk mixture to make sure all chocolate chips have melted. Whisk in powdered sugar. Immediately pour warm chocolate icing over the mint icing and spread with a spatula.

Place brownies in the fridge or freezer until chocolate icing is firm, about 15 to 30 minutes. Cut and serve.