Preheat Oven – Preheat your oven to 350°F (175°C) and lightly grease a 9×13-inch baking dish.
Make the Potato Mixture – In a large mixing bowl, combine the thawed hash browns, cream of chicken soup, sour cream, cheddar cheese, ¼ cup melted butter, onion (if using), garlic powder, salt, and pepper. Stir until well mixed.
Transfer to Dish – Spread the potato mixture evenly into the prepared baking dish.
Prepare Topping – In a medium bowl, mix crushed corn flakes with ¼ cup melted butter until evenly coated.
Top the Casserole – Sprinkle the corn flake mixture evenly over the potatoes.
Bake – Bake uncovered for 45–50 minutes, or until the casserole is hot and bubbly and the topping is golden brown.
Serve – Let it cool for 5 minutes before serving.