01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish.
02 - In a large mixing bowl, combine thawed hashbrowns, shredded cheddar cheese, cream of chicken soup, sour cream, melted butter, chopped onion, garlic powder, salt, and black pepper. Mix until well combined.
03 - Spread the mixture evenly into the prepared baking dish.
04 - In a separate bowl, toss the crushed cornflakes with melted butter until evenly coated.
05 - Sprinkle the cornflake mixture evenly over the casserole.
06 - Bake uncovered for 40-45 minutes, or until the top is golden brown and the casserole is bubbly.
07 - Let rest 5-10 minutes before serving to allow the casserole to set.