Preheat the oven to 350 F and line a 9x13-inch baking dish with foil and spray with non-stick cooking spray.
Prepare and bake the brownie batter according to package directions.
Remove the brownies from the oven and let cool completely. Be patient!
Use the cookie cutter to cut out as many rectangles as possible as close together as possible.
Place the brownies on a serving plate or foil-lined baking sheet.
Heat the Wilton icing in the microwave for 15 seconds and shake.
Gently squeeze the icing from the bottle and carefully outline the brownie.
Then, fill in the icing and use a toothpick to help smooth it out.
Place 4 blue M&M's in the upper right corner of the brownie.
Place 3 red M&M's across the top of the brownies.
Place 3 white M&M's in the middle of the brownie.
Place 5 red M&M's on the bottom of the brownie.
Repeat this process with all the brownies.
Enjoy!