1 (8-ounce) package elbow macaroni (about 2 cups uncooked macaroni) 2 cups milk 1/4 cup all-purpose flour 1 teaspoon onion salt 2 (10-ounce) blocks sharp Cheddar cheese, shredded (about 4 1/2 cups) and divided* 1 cup soft breadcrumbs (4 slices, crusts removed) 1/4 cup butter or margarine, melted Cook macaroni according to package directions; drain well. Set aside. Place milk, flour, and onion salt in a quart jar; cover tightly, and shake vigorously 1 minute. Stir together flo