Peel the potatoes and slice them thin, about ⅛-inch thick. Keep them uniform so they cook evenly. Place slices in cold water to prevent browning while you prepare the sauce.

In a medium saucepan over medium heat, melt the butter. Add minced garlic and cook for about 30 seconds until fragrant. Pour in heavy cream and milk. Stir gently and heat until warm, not boiling.

Season with salt, pepper, and nutmeg. Remove from heat.

Preheat oven to 375°F (190°C). Grease your baking dish with butter.

Drain and pat dry the potato slices. Layer half of the potatoes evenly in the dish. Pour half of the cream mixture over them. Sprinkle half of the cheddar and a bit of Parmesan.

Repeat with remaining potatoes, cream, and cheese.

Cover loosely with foil and bake for 45 minutes. Remove foil and bake an additional 25–30 minutes until the top is golden and bubbling and the potatoes are fork-tender.

Let the dish rest for 10 minutes before serving. This helps the sauce set slightly and makes serving easier.