For 4 people
For 4 people
Preheat the oven to 150°C and butter a gratin dish.
Cut two cheeses into pieces and gently melt them with the milk and cream. Refrigerate or freeze the third cheese so it's easier to cut later.
Peel and wash the potatoes, then cut them into thin slices.
Arrange half of the potatoes in the bottom of the dish and top with half of the cheese mixture. Season with salt, pepper, and rosemary sprigs. Repeat with a second layer of potatoes and the remaining cheese mixture. Season again with salt and pepper.
Slice the remaining cheese into thin slices and place them on top of the dish. Bake for about 50 minutes, until the potatoes are tender.
Serve hot in the baking dish.