Throw a stick of butter and a half cup of flour in a saucepan. Heat at medium heat until melted and bubbling.
Whisk and cook the butter and flour together for a few minutes. This butter and flour is called a roux. The cooking gets rid of the raw flour taste.
WHILE WHISKING, pour some milk into the roux. You have to keep stirring it while you do this so it doesn't lump up. (Worst case scenario, you get lumps and you can take a hand blender to it to smooth it out, but let's just avoid having to wash that by stirring the pot.)
Keep cooking the sauce over medium heat, whisking and stirring in more milk until it is nice, thick and smooth. You've just made a nice white sauce.
Cut your cheese into lumps and throw it in the white sauce. Some people shred the cheese, but since it's melting anyway, why take the time?
Whisk the sauce until the cheese is thoroughly melted and incorporated.
Whisk in the nutmeg.
Bring a pot of water to boil. Sprinkle in some salt (under a teaspoonful). Cook the pasta according to directions on box.
Drain the pasta and leave in pot.
Stir the cheese sauce into the pasta. Cook it all over medium heat for a few minutes to stick it all together. Taste and add a bit of salt and/or pepper if you wish. I tend not to, as the cheese is already salted, as was the pasta water.
If you have time, you can now put this in a baking dish, optionally top with buttered crumbs and bake in the oven. That will make it more solid. It's delicious either way.
A Martone classic! Easy to make, delicious every time. Good to make after a party when you have leftover cheese scraps. I've thrown in everything: parmesan, edam, swiss... go nuts. The kids don't like Swiss so much, so tread lightly on that one.