Melt 2 tablespoons butter in a saucepan over medium heat
Whisk in 2 tablespoons flour and cook for 1 minute
Slowly whisk in 2 cups milk until smooth
Cook, stirring constantly, until the sauce thickens
Lower the heat and add 2 cups shredded cheese
Stir until the cheese is fully melted and smooth
Season with salt, black pepper, and a little mustard powder if desired
Use immediately with cooked macaroni