Preheat the oven to 200°C / 400°F.

Peel the 1.5 kg potatoes and slice them into thin, even rounds, about 2 to 3 mm thick.

Crush the 1 garlic clove and season the potato slices with the crushed garlic, salt, and black pepper.

Arrange the seasoned potato slices tightly in overlapping layers in the ovenproof gratin dish.

Pour the 400 ml heavy cream and 200 ml milk into a saucepan, then add the remaining salt, black pepper, and ground nutmeg.

Heat the cream mixture until steaming and just beginning to simmer, then whisk until the seasonings dissolve.

Pour the hot cream mixture evenly over the layered potatoes until they are nearly covered.

Cover the gratin dish with aluminum foil and bake for 30 minutes at 200°C / 400°F.

Remove the aluminum foil and bake for another 30 minutes, until the potatoes are tender and the top is golden brown.

Turn off the oven and let the gratin rest inside for 15 minutes before serving.