Cheddar Tuna Casserole

1/2 cup chopped onion
2 Tbsp. margarine
1 can cream of celery soup
1/3 cup milk
2 (4 oz.) cup noodles, cooked and drained
1 (6 1/2 oz.) can tuna, drained and flaked
1 (4 oz.) pkg. shredded Cheddar cheese
1/4 cup grated Parmesan cheese
2 Tbsp. chopped pimiento (optional)

Saute onion in margarine; add soup and milk. Stir in remaining ingredients except 1/2 cup Cheddar cheese. Pour into 1 quart casserole. Bake at 350 degrees for 30 minutes. Top with remaining Cheddar cheese and continue baking until melted. This recipe is very easy to double.