1/3 stick butter
1 med. onion, chopped
3 tbsp. flour
1 1/2 c. milk
1 c. shredded American cheese
6 med. potatoes, cooked, peeled and diced

Fry onion in butter until transparent. Blend in flour, gradually add milk. Stir and cook over low heat until thickened. Add cheese. Continue cooking and stirring until cheese is melted. Arrange diced potatoes in greased baking dish. Pour sauce over potatoes. Bake 1 hour at 350 degrees. Top with buttered crumbs, if desired.