Preheat the oven to 350° F; grease a 9x13 pan and set aside.
Cream together butter and sugar in a stand mixer or electric hand mixer. Add eggs one at a time.
Add vanilla and cocoa; mix together until combined.
Add flour one cup at a time and mix until combined. Pour batter in prepared baking pan and bake 30 minutes, or until a toothpick inserted into the center comes out clean. Allow brownies to cool completely before frosting.
Frost the brownies with one of the cans. Add more frosting as desired (I used both cans entirely). Use a sharp knife to lightly score lines to make 12 square brownies. Add Junior Mints to each square to make 12 dice, two in each number (two 1's, two 2's, etc.)
Cover with plastic wrap and place in the fridge. Remove from fridge one hour before serving and cut the brownies. (This will make nice, smooth edges on the brownies and frosting.) Place on a platter to serve, or place in baggies for a take-home treat.