Preheat Oven & Prepare Dish: Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish with butter.
Prepare the Cream Mixture: In a medium saucepan, combine heavy cream, milk, minced garlic, salt, pepper, and nutmeg. Warm over low heat until just hot—do not boil.
Layer the Potatoes: Arrange a layer of potato slices in the prepared dish. Sprinkle a little Gruyère or Cheddar over the layer. Repeat layers until all potatoes and cheese are used, finishing with a layer of cheese on top.
Add Parmesan: Sprinkle grated Parmesan over the top for a golden, crispy crust.
Bake: Cover the dish with foil and bake for 45 minutes. Remove foil and bake for an additional 20–25 minutes, or until the top is golden and bubbly and potatoes are tender.
Rest & Serve: Let the gratin rest for 5–10 minutes before serving to allow the cream to thicken slightly. Garnish with chopped parsley if desired.
Serving and Storage Tips
