Cook macaroni in boiling salted water until almost tender. Meanwhile, in a small saucepan, melt butter. Stir in flour, salt, mustard, pepper and hot pepper sauce. Cook and stir until smooth. Drain macaroni; combine with butter mixture in a large bowl and mix well. Stir in milk and 4 cups of cheese. Pour into an ungreased 13x9x2" baking dish. Cover and bake at 350 degrees for 45 minutes or until bubbly. Sprinkle with remaining cheese; let stand 5 minutes before serving.
