Preheat the waffle iron and grease it lightly with cooking spray.

In a bowl, prepare the brownie batter per the box instructions then stir in 1 additional egg. Scoop about 1/3 cup of batter into the waffle iron and close the lid. Cook the waffle for about 5 minutes then open the lid and remove the waffle. (It may be easiest to remove the waffle one quarter at a time depending on your waffle iron.)

Top the brownie waffle with whipped cream and sprinkles and serve immediately.