Cook 1 lb. pasta and drain. While pasta is cooking, make cheese sauce.
Cheese sauce: Melt 1/2 C. butter over medium heat. Stir in 1/2 C. flour. Slowly whisk in 4 C. milk. Add 1 lb. grated cheddar cheese (or mixture of cheddar and jack or swiss -- whatever you like) and stir until it is nearly melted. Add 1 tsp. salt, 1/4 tsp. white pepper, 1 tsp. dry mustard, a little cayenne (to taste).
Put drained pasta in 13x9 inch baking casserole. Pur cheese sauce over and mix together well. a Sprinkle little chopped parsley and a little paprika on top. Bake at 350 x 30-40 minutes, until top is a little crusty.