1 1/2 c. soda cracker crumbs
6 tbsp. butter, melted
2 tbsp. onion, chopped
1 (6 1/8 oz.) can tuna, drained
1 1/3 c. milk
1 can cream of mushroom soup

Combine cracker crumbs, butter, and onion in a medium bowl. Mix well. Place 1/3 of crumb mixture in a casserole. Cover with half of the tuna fish. Repeat layers, ending with a crumb layer. Pour 1 cup of milk on top.

Bake in a preheated, 400 degree oven 20 minutes. Place soup and 1/3 cup milk in a saucepan. Cook over medium heat until bubbly. Stir often. Pour soup mixture over casserole when ready to serve.