In a large bowl, combine sour cream, cream of chicken soup, 1/3 cup melted butter, salt, garlic powder, onion powder, and pepper. Stir in the thawed hash browns and shredded cheddar cheese until well mixed.
Transfer the potato mixture to a greased 9x13-inch baking dish.
In a small bowl, mix the crushed cornflakes with 1/4 cup melted butter. Sprinkle evenly over the potato mixture.
Bake in the preheated oven for 45-50 minutes, or until the casserole is bubbly and the topping is golden brown. Sprinkle on fresh parsley for garnish.