Preheat the oven to 350 degrees F. Spray an 8x8 inch pan with nonstick baking spray. Place a strip of parchment paper in the pan to cover the bottom and leave a little overhang on two of the sides to use as handles to pull the brownies out of the pan once cooled. Set aside.
Add the butter and baking chocolate to a microwave-safe bowl. Microwave in 30-second intervals and stir after each interval until the chocolate is completely melted.
Pour the butter and chocolate into a large mixing bowl. Add in the granulated sugar, brown sugar, eggs, and vanilla extract. Using a hand mixer, beat on medium for about 1 to 2 minutes until lighter in color and thick.
Add in the cocoa powder, flour, baking powder, and salt. Beat just until the flour is incorporated.
Add dollops of the brownie batter to the prepared pan. Gently spread the brownie batter out evenly using a spatula.
Place in the preheated oven and bake for 28 to 35 minutes until done.
Let cool completely before making the frosting.
Frosting
Add the butter, powdered sugar, mint extract, vanilla extract, milk, and food color to a large bowl. Beat with a hand mixer on low just until the powdered sugar is combined.
Add in the mini chocolate chips and turn the mixer up to medium/high. Beat until fluffy.
Gently spread the frosting evenly on top of the brownies.
Pull the brownies out of the pan using the parchment paper and cut.
Notes
I doubled the frosting recipe for a thicker layer.
If you want your frosting sweeter, add an additional ½ to 1 cup of powdered sugar and ½ to 1 tablespoon of milk to the frosting recipe. Taste to make the mint is still to your liking, if not, add an additional ¼ to ½ teaspoon of mint extract.