In a large mixing bowl, combine the potatoes, cheddar cheese, mozzarella cheese, Parmesan cheese, heavy cream, salt, black pepper, and garlic powder. Mix well.
Transfer the mixture to a greased baking dish and spread it out evenly.
Bake in the preheated oven for 45 minutes, or until the top is golden brown and the potatoes are tender.
Let it cool for a few minutes before serving. Enjoy!
Notes:
This casserole can be made ahead of time and reheated. It's a great dish for potlucks and family gatherings.