In a saucepan, melt butter over medium-low heat. Stir flour into the butter until smooth and bubbly. Stir in salt. Gradually add milk, stirring constantly. continue to cook, stirring constantly, until thickened. Add cheese and continue to cook and stir until melted. In any casserole dish, dot with butter and sprinkle bread crumbs and parmesan cheese. Pour macaroni and cheese into dish. Top with more bread crumbs, parmesan cheese and sharp cheddar. Bake in a preheated 350° oven for 20 minutes, or until hot and bubbly.