1 can (9.5 oz.) Tuna
Celery
1 small onion (optional)
1 can cream of mushroom soup
3/4 soup can of milk
1/2 cup mayonnaise
2 cups sharp Cheddar cheese
2 cups cooked noodles

Combine Tuna, celery, onion, noodles and mayonnaise. Cook soup, 1 1/2 cups of cheese and milk, just until cheese melts. Add other ingredients. Sprinkle remaining 1/2 cup of cheese over top. Bake at 350 F for 25 minutes or until hot.