Preheat the oven to 350°F.
Line a 9x13-inch metal pan with parchment paper.
Melt the butter.
Whisk the melted butter with the granulated sugar and brown sugar until glossy.
Add the eggs one at a time, mixing well after each.
Stir in 1 tablespoon vanilla extract.
Mix in the cocoa powder, salt, and baking powder.
Fold in the flour just until combined.
Stir in the chocolate chips.
Spread the batter evenly into the prepared pan.
Bake for 28 to 34 minutes.
Cool the brownies completely.
Chill the brownies for 45 minutes.
Beat 1 cup softened butter, powdered sugar, 2 to 3 tablespoons heavy cream or milk, and 1 teaspoon vanilla extract until fluffy.
Divide the frosting and color it with gel food coloring.
Lift the chilled brownies from the pan.
Cut the brownies into rectangles.
Frost each brownie rectangle.
Add 4 to 6 M&M’s on top of each brownie in neat rows.
Chill briefly to set.