Upper crust (5)
'upper crust' is the definition.
(elite is a kind of upper crust)
This is the entire clue.
(Other definitions for elite that I've seen before include "12 letters = 1 inch (type)" , "Identified as the best" , "Exclusive set" , "Aristocratic" , "type in pool?" .)
(Other definitions for gratin that I've seen before include "Au . . . . . . means cooked with melted cheese" , "Cooked covered in grated cheese or breadcrumbs" , "A dish cooked with grated cheese on it" , "Grated cheese or breadcrumbs on a dish" , "Au . . . . . . - cooked with a crust of melted cheese" .)