Dishes covered with breadcrumbs or grated cheese (2,6)

(Other definitions for au gratin that I've seen before include "baked with a coating of breadcrumbs" , "Cooked, covered with breadcrumbs" , "Of food dish, cooked with crust of melted cheese" , "Cooked with grated cheese and/or breadcrumbs" , "Cooked covered with cheese" .)