Preheat the Oven:
Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Prepare the Mixture:
In a large mixing bowl, combine the sour cream, cream of chicken soup, melted butter, garlic powder, onion powder, salt, and pepper. Mix until smooth.
Add Potatoes and Cheese:
Fold in the diced potatoes (or frozen hash browns) and 1½ cups of shredded cheddar cheese. Stir until everything is evenly coated.
Assemble the Casserole:
Transfer the mixture to the prepared baking dish, spreading it out evenly.
Optional Topping:
If using a topping, mix the crushed cornflakes or breadcrumbs with 2 tablespoons of melted butter. Sprinkle over the top of the casserole.
Bake:
Cover the casserole with foil and bake for 30 minutes. Remove the foil, sprinkle the remaining ½ cup of cheese on top, and bake uncovered for an additional 15-20 minutes, or until the cheese is bubbly and the edges are golden brown.
Cool and Serve:
Let the casserole sit for 5-10 minutes before serving.