Preheat oven to 350 degrees. Melt the butter in a large skillet. Saute the onions in the butter. Boil beans in chicken broth for 10 minutes, then run under cold water and drain. Add the beans, mushroom soup, onion rings and salt and pepper. Stir well. Pour onto greased 1 ½ quart baking dish. Bake for 20 minutes, then top the casserole with the Cheddar cheese and bake for 10 minutes, or until cheese is melted.
If you can use a foil pan so you do not have to clean the dish. 🙂