Allow the cubed hashbrowns to thaw in the refrigerator overnight, or for several hours on the countertop.
Preheat the oven to 350ºF and grease a deep 9X13 baking dish with cooking spray.
In a large bowl, combine the sour cream, cream of chicken soup, and ½ cup of melted butter. Fold them together with a silicone spatula.
Add the salt, onion powder, and pepper. Fold it into the soup mixture to combine.
Add in shredded cheddar cheese and fold again.
Finally, add in the thawed hash brown potatoes. Stir the mixture together until all of the potatoes are coated with the soup mixture.
Pour the potato and soup mixture into the greased casserole dish, spreading it into an even layer.
Crush the cornflakes by placing them in a plastic storage bag and pressing them firmly with a rolling pin.
Melt the butter in a medium-sized bowl in the microwave using 30-second intervals.
Once the butter is melted, add the crushed Corn Flakes to the melted butter and stir to coat.
Sprinkle the crushed Corn Flake and butter mixture on top of the casserole, ensuring the topping is evenly distributed.
Place the dish in the oven and bake uncovered for 40-50 minutes, or until hot and bubbly.
Remove from the oven and allow it to cool for 5-10 minutes before serving.