• Preheat oven to 325 degrees. Line a 9 x 9" baking pan with parchment paper, with the sides folded over the edges of the pan. Set aside.
• In a microwave safe mixing bowl, melt the butter in the microwave. In a seperate bowl, combine the granulated sugar, cocoa powder and salt. Mix to combine and then gradually stir into the butter until smooth. (If mixture is still hot from the melted butter, let cool for a few minutes before adding the eggs.) Whisk in the eggs, and add the mint extract to the batter. Combine the flour and baking powder, and gradually add into the batter. Stir until completely combine and smooth.
• Pour batter into the parchment lined pan, and spread evenly. Bake the brownies for 35-40 minutes or until toothpick inserted comes out with crumbs. Center may look slightly underdone, but the brownies will be cooked through. Remove brownies from the oven and let cool completely.

Mint Buttercream Frosting:

• Combine the softened butter with 1/2 cup scoops of powdered sugar. Using a hand or stand mixer, gradually add the 1/2 cups of powdered sugar in, occasionally adding a tablespoon of milk if necessary to get a thick, smooth frosting. Once all of the powdered sugar has been added, add the mint extract and food coloring to the frosting and mix until the desired color of green is achieved. (I used about 3-4 drops of green food coloring to get a mint-green color.)
• Lastly, evenly frost the cooled brownies with the mint buttercream frosting. Top the frosting with the Thin Mint Cookies, Andes Mint chocolates, and chocolate chips.
• Refrigerate about 1 hour to let the frosting set before slicing. Leftovers can be kept in an airtight container at room temperature for up to 5 days.