Preheat your oven

Start by preheating your oven to 350°F. Lightly grease a 9x13-inch casserole dish with non-stick cooking spray to prevent sticking.

Mix the casserole base

In a large mixing bowl, combine the thawed hashbrowns, 1 ½ cups of shredded cheddar cheese, cream of chicken soup, sour cream, melted butter, diced onion (if using), garlic powder, salt, and pepper. Stir until everything is evenly combined.

Transfer to the baking dish

Spread the hashbrown mixture evenly into your prepared casserole dish. Smooth it out with a spatula to ensure even cooking.

Add the topping

If you’d like a crunchy topping, mix the crushed cornflakes or breadcrumbs with 2 tablespoons of melted butter. Sprinkle this mixture over the top of the casserole.

Bake until bubbly

Bake the casserole in the preheated oven for 45–50 minutes, or until the top is golden and the edges are bubbling.

For an extra cheesy finish, sprinkle the remaining ½ cup of cheddar cheese over the top during the last 5 minutes of baking.

Let it rest

Once baked, let the casserole cool for 5–10 minutes before serving. This helps it set and makes it easier to scoop.