Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking dish.
In a large bowl, combine the thawed diced potatoes, cream of chicken soup, sour cream, 1.5 cups of cheddar cheese, 0.25 cup melted butter, onion, salt, and pepper. Mix well.
Transfer the mixture into the prepared baking dish, spreading it evenly.
In a separate bowl, combine the crushed cornflakes with the remaining 0.25 cup of melted butter. Sprinkle over the potato mixture.
Bake in the preheated oven for 35 minutes. Remove from oven, sprinkle the remaining 0.5 cup of cheddar cheese on top, and bake for an additional 10 minutes until cheese is melted and bubbly.
Allow to cool for a few minutes before serving. Enjoy!
Notes
Adjust seasoning to taste. For an added twist, you can mix in chopped green onions or crumbled bacon.