1) Baked with a cheese crust 2) Baked with a cheese topping 3) Baked with cheese on top 4) Cooking term 5) How potatoes may be served 6) Like some potatoes 7) One way to cook 8) One way to prepare potatoes 9) One way to serve potatoes 10) Popular way to serve potatoes 11) With cheese baked on top 
• With a crust made by browning in the oven; as, spaghetti may be served au gratin.
(o gra-tang). Literally, dressed with brown crumbs. In actual practice, also flavored with grated cheese.
Au` gra`tin' [ French] (Cookery) With a crust made by browning in the oven; as, spaghetti may be served au gratin . 
Recipes that are browned in the oven, or under a grill. Often refers to dishes that use a sauce and are topped with breadcrumbs and/or cheese.
Baked with cheese and breadcrumbs
In cookery, au gratin refers to sprinkled with breadcrumbs and grated cheese and browned. Sometimes a dish may be just sprinkled with breadcrumbs and sometimes just grated cheese, but all three combinations are known as au gratin.
[adj] - cooked while covered with browned breadcrumbs (and sometimes cheese)
adjective cooked while covered with browned breadcrumbs (and sometimes cheese)
cooked or baked with a topping of either browned bread crumbs and butter or grated cheese, or with both.