Turn your oven on to 370 degrees right now. Brush your baking dish with plenty of melted butter. This makes the bottom layers very crispy and golden.

Peel your potatoes and wash them in cool water. Use a mandoline to cut them into thin circles. The slices must be very thin to stack well.

Whisk the heavy cream and minced garlic in a bowl. Add the fresh thyme leaves and the black pepper. This liquid will flavor every single potato layer.

Place a single layer of potatoes in the dish. Sprinkle a little salt and some shredded Gruyere cheese. Pour a small amount of cream over the top.

Keep adding layers until you reach eleven total layers. Press down on the potatoes to keep them tight. This creates the famous dense and creamy texture.

Cover the dish with foil and bake for forty minutes. Remove the foil and add the salty Parmesan cheese. Bake for fifteen more minutes until the top bubbles.