Heat Guinness in a small saucepan over medium/high heat for about 12 minutes. You are making a reduction, so the beer should reduce to about 1/3 cup in this amount of time. Take off of heat and set aside.

Mix brownie box ingredients according to package instructions. If the box gives you the option of fudgy vs. cake brownies, go with fudgy.

Add Guinness reduction to batter and stir completely. Add chocolate chips and stir to combine.

Cook brownies according to package instructions.

Remove from oven and allow to cool completely.

Using an electric mixer, beat butter until creamed. Add in the powdered sugar one cup at a time. Add milk and continue to beat until fluffy icing forms. Add in the mint extract and food coloring (optional).

Once brownies are completely cool, Ice with icing and place in the fridge for 30 minutes to allow the icing to set.

Cut and serve. Enjoy!