Root vegetable gratin is a hearty and comforting dish that combines layers of thinly sliced root vegetables with a creamy and cheesy sauce. The gratin is made by layering sliced potatoes, sweet potatoes, carrots, and parsnips in a baking dish. A mixture of cream, cheese, garlic, and herbs is poured over the vegetables, and the dish is baked until the vegetables are tender and the top is golden and bubbly. Serve this gratin as a side dish or a vegetarian main course.