Preheat your oven to 350 degrees F (175 degrees C).
In a large bowl, combine the thawed hash browns, Cheddar cheese, sour cream, condensed cream of chicken soup, half of the melted butter, onions, salt, and black pepper. Mix everything well until evenly combined.
Transfer the potato mixture into a greased 9x13-inch baking dish.
Scatter the crushed cornflakes over the top, and then drizzle the remaining melted butter evenly across the top.
Place the dish in the preheated oven and bake for 1 to 1 ½ hours, or until the top turns golden and the mixture is bubbling at the edges.
Remove from the oven, let it cool slightly, and serve hot. Enjoy!