This is the perfect entertaining recipe because of the versatility of cutting the brownies into FUN shapes!
Preheat oven to 350 degrees. Line a 9x11 baking pan with foil and spray with cooking spray.
Mix cake mix, egg, softened butter and vanilla until blended. Fold in 1/2 of the M&M's.
Press batter into the prepared pan and sprinkle with the remaining M&M's.
Bake for 35-40 minutes or until toothpick inserted comes out clean.
Then the FUN part comes! After the brownies have cooled, remove them from the pan and cut them into squares or be fancy and use a cookie cutter!