Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the thawed hash browns, sour cream, cream of chicken soup, shredded cheddar cheese, melted butter, garlic powder, onion powder, salt, and black pepper. Mix well until all ingredients are evenly combined.
Spread the mixture evenly into a greased 9x13-inch baking dish.
In a separate bowl, combine the crushed cornflakes with 2 tablespoons of melted butter. Stir until the cornflakes are well-coated.
Sprinkle the cornflake mixture evenly over the top of the potato mixture in the baking dish.
Bake in the preheated oven for 45-55 minutes, or until the top is golden brown and the edges are bubbly.
Remove from the oven and let it cool for about 10 minutes before serving.