Preheat your oven to 375°F and grease a 9x13 baking dish.
If there's large chunks of hashbrowns frozen together, break them up. I like to drop the bag on the countertop a few times.
In a large bowl, combine frozen hashbrowns, cream of chicken soup, 2 cups of cheese, diced onions, salt, pepper, sour cream, and melted butter. Mix until everything is evenly coated.
Transfer the mixture to your prepared baking dish and spread it out evenly.
Sprinkle the remaining 1 cup of cheese on top.
Cover with foil and bake for 1 hour.
For a golden, bubbly finish, remove the foil and broil for the last couple of minutes—watch closely so it doesn’t burn!
