Melt the butter over medium heat in a large skillet or the same pot you cooked the macaroni in.
Whisk in the flour and cook for 3 minutes, whisking constantly.
Slowly pour in the milk, 1/2 cup at a time, and whisk. Whisk steadily for about 10 minutes until any lumps are gone and the mixture is nice and creamy smooth.
Remove from heat and add the salt, pepper, cayenne (if using) and 2 cups of the cheese. Stir until the cheese has melted.
Line a 9" x 13" baking dish with parchment or wax paper.
Pour in the macaroni and cheese and level out with a spatula.
Let cool before placing into the fridge for at least eight hours.
For the mac-and-cheese waffles
Heat your waffle iron and spray well with non-stick spray.
Working in batches, cut the macaroni and cheese into whatever sizes and shapes you want.
Sprinkle a bit of cheese on the waffle iron and add the macaroni and cheese. Top with a bit more cheese and close the waffle iron. Do not press down. Cook 5-6 minutes.
Turn off the waffle iron and let cool 5-10 minutes or until you can remove the mac-and-cheese without it sticking. Keep warm in the oven on low as you cook the remaining mac-and-cheese.