Preheat your oven to 350 degrees and line a 9×13 dish with parchment paper and lightly grease.
Make brownies as instructed on the box and bake in the 9×13 dish.
Beat the powdered sugar, butter, mint extract, food coloring and milk until smooth in a medium bowl. Spread evenly over the cooled brownies (we add dollops all over the top to make it easier to spread).
In a microwave safe bowl, melt chocolate chips and butter until smooth.
Spread over. the mint layer, cover and chill for at least 1 hour.
Let set out for 20-30 minutes before cutting into squares.