Preheat your oven to the temperature listed on your brownie mix box (typically 350°F/175°C).
Lightly grease a 9x9-inch baking pan with cooking spray.
Prepare the brownie batter as instructed on the package and pour into the prepared pan.
Bake according to the package directions. Remove from oven and let cool completely.
In a large bowl, beat the butter and cream cheese until light and fluffy.
Add the peppermint extract, salt, and powdered sugar. Mix until smooth.
Stir in the heavy cream and a few drops of green food coloring, if using. Mix well.
Spread the mint frosting evenly over the cooled brownies. Chill for 15–20 minutes to firm up.
In a microwave-safe bowl, combine chopped chocolate and Andes mints. Microwave in 30-second intervals, stirring until smooth.
Let the chocolate cool for about 3 minutes, then pour over the mint frosting layer and spread evenly.
Refrigerate for about 30 minutes, or until the chocolate topping is set.
To slice, run a sharp knife under hot water, wipe dry, and cut into squares. Repeat between cuts for clean slices.
Serve and enjoy every fudgy, minty bite!