au gratin means: A French term that describes a dish with breadcrumbs or cheese browned on top; (in Cooking Dictionary)
What else does au gratin mean?
French-style food is served with sauce, sprinkled with cheese or crumbled, and butter topped with it. (in Cooking Dictionary)
Loaded with butter, crumbs, or grated cheese and covered. Then baked in the oven. (in Merlin Dictionary)