Preeat oven to 350.
Melt 3 T. butter in saucepan over low heat (I usually cook mine in a Le Creuset dutch oven-like pot so it's a one-pot meal).
Blend in flour and salt; cook and stir for 1 minute.
Slowly add milk and then pepper, dry mustard, and hot sauce; whisk/stir constantly until thickened.
Add shredded cheese (reserve 1/2 c. or so for topping) and stir until cheese is melted.
Mix pasta and cheese sauce in 2 qt.casserole dish. Sprinkle remaining cheese on top.
For topping: mix melted butter with bread crumbs and sprinkle on the top.
Cover and bake in 350 degree oven for 20 minutes.