Just made some yesterday at the request of my kids. Boil the pasta and grate a bunch of cheese, mix of whatever you have, hopefully some is sharp. Pour the pasta out into a colander (actually mine was half cauliflower, also at request of the kids). Put a whole stick of butter (had 1lb dry pasta plus a lot of cauliflower) in the pot and back on medium heat. Into melted butter put flour to make a light roux. Once that is ready, add milk slowly, whisking continuously until you have a sauce like for biscuits and gravy. Then add the cheese, let it all melt, keep stirring but with wooden spoon; stir in some mustard and any other seasonings you want, then the pasta.

Into buttered dish, topping (I used bread crumbs, shredded cheese works, crushed potato chips also work, or any combination of these) bake at 400f or so until the top is golden.

So good, not healthy even with cauliflower.