Make the brownies according to the directions on the package.
While the brownies are in the oven, unwrap and chop the Andes mints into small pieces.
Remove the cooked brownies from the oven and sprinkle all the Andes mints on top. Let sit for 2-3 minutes to melt, then use an off-set spatula or butter knife to spread the chocolate in an even layer across the brownies.
Let the brownies cool entirely, then cut into squares and serve!