Cook macaroni according to package directions until almost tender. Meanwhile, in a large stock pot, melt 1 cup butter. Stir in flour and salt until smooth. Gradually stir in milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Reduce heat. Add cheese, stirring until melted. Drain macaroni; stir into sauce.
Transfer to three greased 13-in. x 9-in. baking dishes. Melt remaining butter; toss with bread crumbs. Sprinkle over casseroles.
Bake, uncovered, at 350° for 35-40 minutes or until golden brown. Yield: 36 servings (1 cup each).