Making Baked Hash Brown Casserole is as simple as following these step-by-step instructions:

1. Preheat your oven to 350°F (175°C).
2. Prepare a baking dish by greasing a 9×13-inch casserole dish with cooking spray or butter.
3. Mix Ingredients: In a large bowl, combine the thawed hash browns, sour cream, cream of chicken soup, shredded cheddar cheese, chopped onion, melted butter, garlic powder, salt, and black pepper. Mix everything together until well combined.
4. Spread the Mixture: Pour the mixture into the prepared casserole dish and spread it evenly.
5. Add Topping: If desired, sprinkle the crushed cornflakes on top for added crunch.
6. Bake: Place the casserole in the preheated oven and bake for 45-50 minutes, or until the edges are bubbly and the top is golden brown.
7. Cool and Serve: Remove the casserole from the oven and let it cool for a few minutes before serving.

By following these steps, you will have created a delicious Baked Hash Brown Casserole that everyone will love.