This Is the ultimate comfort food and easy to make at home!
Meanwhile, in a large pot melt the butter over medium-low heat. Add the flour and quickly whisk. Cook for about 3 minutes, whisking frequently, or until smooth and slightly browned. Be careful not to burn the mixture. Add 1 cup of the milk and whisk until well combined and there are no lumps. Add the remaining milk and keep whisking until the mixtures starts to boil.
Add 3 cups cheddar cheese, all the Gruyere cheese, dry mustard, salt, and pepper and stir until cheese is melted and smooth.
Sprinkle the remaining 1 cup cheddar cheese over the top of the macaroni and then add the panko cracker topping.