资料来源 : Webster's Revised Unabridged Dictionary (1913)

Au gratin \Au` gra`tin"\ [F.] (Cookery)
   With a crust made by browning in the oven; as, spaghetti may
   be served au gratin.

资料来源 : WordNet®

au gratin
     adj : cooked while covered with browned breadcrumbs (and sometimes
           cheese)