In a medium saucepan filled with boiling water, cook macaroni until al dente, about 7-8 minutes. Drain.
Melt 2 tablespoons of butter in the same pot over low heat. Add milk and cheese packet and whisk well. Turn off the heat and return macaroni to pot. Add 1 cup cheddar and stir until the cheese has melted and the macaroni is evenly coated in the cheese sauce. Stir in egg and bread crumbs until evenly combined.
Meanwhile, preheat the waffle iron. When the waffle iron is hot, spray with cooking spray. Scoop about ½ cup of the macaroni and cheese into the center of the grate and sprinkle with more cheese. Close the iron and cook until golden and crispy, about 5 minutes. Use forks to carefully remove the waffle from the iron. Repeat until you’ve used up all the macaroni and cheese.