Slice the potatoes into thin rounds (about 2–3 mm / ⅛ inch thick). A mandoline is helpful here, but a sharp knife works as well.

Cut one garlic clove in half and rub the inside of a baking dish with the cut side. Then grease the dish with butter.

In a large pan, heat the milk and cream over medium heat. Season with nutmeg, salt, and pepper. Stir in the Dijon mustard and finely chopped or pressed garlic.

Add the sliced potatoes to the pan and bring to a gentle boil. Simmer for about 10 minutes, until the potatoes just begin to soften.

Use a slotted spoon to transfer the potato slices into the prepared baking dish. Pour the milk–cream mixture over the top so the potatoes are fully covered.

Sprinkle with grated cheese and dot the surface with small pieces of butter.

Bake for 30–40 minutes, until the top is golden brown and the potatoes are cooked through.

Let the gratin cool for a few minutes before serving so it firms up slightly. Garnish with fresh or dried parsley, if desired. Enjoy!