Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large mixing bowl, combine the thawed hash browns, sour cream, cream of chicken soup, French onion dip, 1 cup of cheddar cheese, Parmesan cheese, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Spread the mixture evenly into the prepared baking dish.
In a separate bowl, combine the crushed cornflakes and melted butter. Mix until the cornflakes are evenly coated.
Sprinkle the cornflake mixture over the top of the potato mixture in the baking dish.
Bake in the preheated oven for 45-50 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.