In a large skillet, cook the chopped onion in the butter or margarine. Mix in 1 lb ground beef and cook until browned. Drain off any excess fat. Stir in the tomato soup, 1 cup water, the macaroni, and cook until macaroni is tender. You can add a can of creamed corn if you think you might like it. Pour into a casserole dish, bake uncovered 25 minutes, at 350 degrees. Sprinkle with grated cheddar, bake another 20 minutes.