Preheat the oven to 375°F (190°C).
Grease a baking dish with butter.
Layer half of the sliced potatoes in the dish.
In a saucepan, combine heavy cream, garlic, salt, pepper, and nutmeg, heating gently.
Pour half of the cream mixture over the first layer of potatoes.
Sprinkle half of the cheddar and Parmesan cheeses on top.
Repeat the layering with the remaining potatoes, cream, and cheese.
Dot the top with remaining butter.
Cover with aluminum foil and bake for 40 minutes.
Remove foil and bake for an additional 20 minutes, until golden and bubbly.