Combine all ingredients except spaghetti and butter in crockpot; stir well. Cover and cook on Low for 6 to 8 hours.
Just before serving, cook spaghetti according to package directions; drain and toss with butter. Stir into crockpot. Sprinkle additional grated cheese over top. Serves 4.
This recipe may be doubled for the 5 quart crockpot.