Peel the potatoes and rinse them under cold water.

Slice them very thin (about ⅛ inch thick) using a mandoline slicer or a sharp knife.

Do not rinse after slicing to keep the natural starch, which helps the gratin bind together.

In a saucepan, combine heavy cream and whole milk.

Peel the garlic cloves, crush them lightly, and add them to the mixture.

Add salt, pepper, and nutmeg (if using) and heat gently without boiling.

Butter a baking dish generously, ensuring the sides are coated.

Arrange the potato slices in even layers for consistent cooking.

Remove the garlic from the cream mixture, then pour the warm liquid over the potatoes, covering them completely.

Preheat the oven to 320°F (160°C).

Dot the top of the gratin with small pieces of butter for a light golden finish.

Bake for 1 hour, or until the potatoes are tender (test with a knife).

Let the gratin rest for 5 minutes before serving to allow it to set properly.