Preheat oven to temperature listed on brownie mix (325 degrees F in my case). Spray an 8″ square baking dish with cooking spray.
Stir together egg, oil, coffee, and peppermint extract. Add brownie mix, and stir until well mixed. Stir in white chocolate chips, and pour brownie batter into prepared pan.
Generously sprinkle M&M’s over the top of the batter. Bake in preheated oven as directed on the brownie mix. Allow to cool in pan before cutting.
To dust with sugar, hold a mesh strainer over the brownies, and sprinkle about two tablespoons of powdered sugar into the strainer, moving the strainer around as you sprinkle to cover the brownies evenly. The sugar will hide any cracked M&M’s and also looks festive for the holidays.