Meanwhile, prepare the creamy sauce. In a saucepan, combine the crème fraîche and milk, then season with a pinch of nutmeg, salt, and pepper. Heat over low heat until the mixture is smooth, but do not boil to preserve its creamy texture. This sauce will coat the potatoes and meat for a melt-in-the-mouth, flavorful result.
Preheat the oven to 180 degrees Celsius. Butter a suitable-sized baking dish and start by arranging a layer of thinly sliced potatoes. Cover this first layer with some of the ground beef, then pour a little sauce over it. Repeat this process in successive layers until you run out of ingredients, finishing with a layer of potatoes topped with sauce. Sprinkle the gratin generously with grated cheese to create a golden, gratinated crust during baking.
Bake the gratin for about 45 to 50 minutes, until the top is golden brown and the potatoes are tender. You can check the doneness by pricking the gratin with the tip of a knife: it should dig in easily. For an even crispier surface, you can place the gratin under the grill for a few minutes, watching carefully so as not to burn the cheese.
During cooking, the combination of potato and meat layers allows the flavors to blend. The cream soaks into the potatoes, while the meat releases its juices, creating a perfect harmony between melting textures and savory flavors. The cheese gratin adds a crispy, slightly nutty note that contrasts pleasantly with the melting texture of the gratin.
To serve, let the gratin rest for a few minutes after removing it from the oven. This allows the layers to stabilize and makes it easier to cut into neat portions. You can serve this gratin with a lightly dressed green salad to bring freshness and balance to the meal. Fresh herbs such as parsley or chives can also be sprinkled on top to add color and flavor.
Variations can be considered to enrich the gratin according to tastes and seasons. For example, adding sautéed mushrooms to the filling adds extra texture and an earthy flavor. Sliced carrots or zucchini can also be interspersed between the potato layers for a more colorful and nutritious gratin. For a spicier version, a little paprika or sweet chili can be added to the meat.
