Hash Brown Potato Casserole

1 32oz package frozen hash brown potatoes, thawed
3/4 c butter or margarine, melted
1/2 c chopped onion
1 10 3/4oz can cream of chicken soup, undiluted
1 8oz carton commercial sour cream
1 c (4oz) shredded cheddar cheese

Combine potatoes, 1/2 cup butter, onion, soup, sour cream, and cheese. Stir well. Spoon into a greased 2 1/2-quart casserole. Bake at 350° for 50 minutes.