Prepare the potatoes

• Peel and thinly slice the potatoes.
• Let them rest in a bowl of water for a few minutes, then drain and pat dry.

Make the cream mixture

• In a bowl, combine the heavy cream and melted butter.
• Crush the garlic into a paste and stir it into the cream.

Layer the gratin

• Lay a layer of potato slices in the casserole dish.
• Pour over some of the cream mixture, then scatter Gruyère, salt, pepper, thyme and rosemary.
• Repeat the layers a few times, finishing with the remaining cheese.

Bake covered

• Cover the dish and bake at 180 °C for about 1 h 20 min.

Broil and serve

• Uncover and broil for 5 minutes until the top is golden and bubbling.