1. Preheat oven to 400 degree F. Line a 13x9 baking dish with parchment paper. Set aside.
   

Brownies

1. In a small saucepan over medium high heat, combine butter, cocoa powder and oil. Bring to a boil, whisking continuously, and remove from heat.
2. In a large mixing bowl, combine the granulated sugar, eggs, and buttermilk. Slowly add in the butter mixture. Do not over-mix. Add in the flour, baking soda, and salt, stirring just until combined.
3. Fold in Andes mints.
4. Pour into prepared dish and bake for 20 minutes. Remove from oven and cool.
5. Once cooled, prepare the frosting.

Frosting

1. In a large mixing bowl, using an electric mixer, beat butter for 3-4 minutes. Do this until the butter becomes pale in color (important for the whipped texture). Add in milk, sugar, peppermint and food coloring. Beat an additional 3-5 minutes until frosting is light and fluffy. You can add more milk if needed. The ½ cup milk was perfect for me. Fold in chocolate chips.
2. Spread over cooled brownies. Refrigerate for two hours, until set. Cut and enjoy.