Creating the perfect Cheesy Potato Casserole is easy when you follow these simple steps:

1. Preheat the Oven: Start by preheating your oven to 350°F (175°C).
2. Prepare the Baking Dish: Grease a 9×13-inch baking dish to prevent sticking.
3. Mix the Ingredients: In a large mixing bowl, combine the diced potatoes, onions, sour cream, cream of mushroom soup, melted butter, garlic powder, salt, and black pepper. Stir until everything is well combined.
4. Add Cheese: Fold in 1 1/2 cups of shredded cheddar cheese into the potato mixture.
5. Transfer to Baking Dish: Pour the mixture into the greased baking dish, spreading it evenly.
6. Top with Cheese: Sprinkle the remaining 1/2 cup of cheddar cheese on top of the casserole.
7. Crushed Cornflakes: If using, sprinkle the crushed cornflakes over the cheese for a crunchy topping.
8. Bake: Place the casserole in the preheated oven and bake for 45 minutes, or until the top is golden brown and bubbly.
9. Cool Before Serving: Remove from the oven and let it sit for about 10 minutes before serving, allowing the flavors to meld.

By following these steps, your Cheesy Potato Casserole will turn out incredible, ready to impress everyone at your Easter gathering.