Hash Brown Potato Casserole

30 oz. frozen hash brown-style potatoes

2 c. shredded cheddar cheese

1/2 c. chopped onion

1/2 c. butter

16 oz. sour cream

1 tsp. salt

1/4 tsp. pepper

Melt butter in a saucepan over low heat. Add cheese and stir until melted. Remove from heat. In a large bowl, mix sour cream, onion, salt, and pepper. Add butter and cheese mixture. Mix in potatoes. Spread in a large greased casserole dish. Dot the top slightly with additional butter if desired. Bake at 350 degrees for 30 minutes.