1 (7 oz.) Package of elbow macaroni

½ cup minced onion

1/3 cup butter

1/4 teaspoon dry mustard

1 teaspoon salt

1/4 teaspoon white pepper

1/3 cup flour

3 1/4 cups milk

12 oz. shredded Cheddar cheese

Cook macaroni according to package directions and drain. Saute onions in butter until tender. Stir in mustard, salt, white pepper, and flour. Cook 1-2 minutes. Gradually stir in milk, blending well. Bring to a boil, stirring constantly. Reserve ½ cup cheese. Stir remaining cheese into sauce until melted. Stir macaroni into sauce. Pour mixture into 1 ½-quart casserole dish. Sprinkle reserved cheese over top. Bake at 400 degrees for 30-40 minutes. Until heated through and browned on top.