A gratin is a baked dish, usually of vegetables, topped with a breadcrumb and cheese topping. Although gratins came from France, these days they're just as American as apple pie! Though admittedly a bit out of fashion, creamy baked vegetable gratins, such as this one, make a nice side dish when you want something heavy and filling. Try this unique mushroom gratin recipe for a French inspired creamy vegetable side dish. If you like mushrooms, you'll really enjoy this mushroom gratin as a side dish to your vegetarian meal.