Preheat oven to 350°F. Butter large, shallow baking dish or gratin pan. In medium bowl, whisk together cream and chipotle.
Peel potatoes and slice very thinly, using mandolin if possible.
Arrange one layer of overlapping potatoes in bottom of dish. Top with half of onion slices and cover evenly with one-third of cream mixture and one-third of cheese; Season with salt and pepper, to taste.
Repeat procedure for second layer. For top layer, arrange potatoes and top with remaining cream and cheese; season with salt and pepper.
Cover with foil and bake 30 minutes. Remove foil and bake 25 to 35 minutes, until bubbling and golden brown and potatoes are tender. Let cool before serving.
The gratin can be made early in the day and reheated when you reach your destination. After preparing, cover and chill. Reheat, covered, in a 400°F oven, until hot, about 15 minutes.