Preheat your oven to 375°F (190°C) and grease an oven-safe baking dish.

Peel and slice the potatoes thinly. Soak in cold water.

Clean the leeks and slice them thinly.

Melt butter in a skillet, sauté leeks for 3-4 minutes, then add garlic and cook for another minute.

Pour in white wine and let it reduce, then add heavy cream, salt, and pepper, and simmer until slightly thickened.

Stir in three-quarters of the grated cheese until melted.

Layer the gratin by spreading a bit of creamy mixture, half of the potatoes, and half of the remaining cream mixture. Repeat and finish with potatoes and sauce.

Top with remaining cheese and cover with foil.

Bake for 30 minutes, remove foil, and bake for another 20 minutes until golden.

Let cool for 5-10 minutes before serving.