Now we're going to whip up icing. Make sure your butter is softened, not melted. Whip butter in a bowl until smooth and then slowly add a cup of powdered sugar (making sure that the mixture is smooth and there aren't any butter chunks). Once mixed, slowly incorporate 1/4 cup of Creme de Menthe and then the additional cup of powdered sugar. If icing is too thick, add additional Creme de Menthe. Ice squares or full pan of brownies and then sprinkle with remaining half bag of Andes baking chips. Serve and enjoy!