Preheat your oven to 350°F (175°C) and grease a 13x9 inch baking pan.

In a large mixing bowl, combine thawed frozen hash browns, sour cream, diced onion, cream of chicken soup, 1 ½ cups of shredded cheddar cheese, melted butter, salt, and pepper, mixing until well combined.

Pour the mixture into the prepared baking pan and spread it out evenly.

Bake uncovered for 45 minutes, watching for bubbling edges and slight golden color.

Sprinkle remaining ½ cup of cheddar cheese on top and bake for an additional 10 minutes until melted and golden.

Let the casserole rest for about 10 minutes before serving.