Making Million Dollar Potato Casserole is straightforward and satisfying when you follow these steps:

1. Preheat the Oven: Begin by preheating your oven to 350°F (175°C).
2. Prepare Potatoes: In a large pot, bring salted water to a boil. Add the diced potatoes and cook until tender, about 15-20 minutes. Drain and set aside.
3. Mix Ingredients: In a large bowl, combine sour cream, cream of chicken soup, half of the cheddar cheese, melted butter, chopped onion, minced garlic, salt, pepper, and garlic powder. Mix well until combined.
4. Combine Potatoes: Gently fold the drained potatoes into the sour cream mixture, making sure the potatoes are well-coated.
5. Transfer to Baking Dish: Pour the potato mixture into a greased 9×13-inch baking dish, spreading it evenly.
6. Top with Cheese: Sprinkle the remaining cheddar cheese and mozzarella cheese on top for an extra cheesy goodness.
7. Optional Topping: If desired, add crushed cornflakes on top for a crispy texture.
8. Bake: Place the dish in the preheated oven and bake for 40-45 minutes, or until bubbly and golden brown on top.
9. Cool and Serve: Once baked, allow the casserole to cool for about 10-15 minutes before serving. This helps the flavors meld beautifully.

These steps will guide you in creating an amazing Million Dollar Potato Casserole that your loved ones will not soon forget.