Boil the pasta in salted water until al dente, then drain. Don’t overcook—mushy mac is sad mac.
Melt butter in a saucepan over medium heat. Stir in flour to make a quick roux and cook for 1 minute to lose that raw flour taste.
Pour in milk gradually, whisking to keep it smooth. Simmer until the sauce thickens a bit—you want it to cling to the pasta, not slide off like a slippery eel.
Add cheddar (and the optional mozzarella or Parmesan if you’re feeling fancy). Stir until the cheese is melted and the sauce is silky. Season with salt, pepper, and paprika or mustard powder if you’re using them.
Combine the cooked pasta with the cheese sauce. Stir until every elbow is coated. If the sauce is too thick, splash in a bit more milk until you hit that perfect creaminess.
Taste and adjust. If you want more zing, a tiny pinch of cayenne or hot sauce does wonders. Serve hot and gooey.