Crossword Genius

Mark, when cycling, gets a crusty dish (6)

Ross

I believe the answer is:

gratin

'crusty dish' is the definition.

I don't understand how the rest of the clue works.

(Other definitions for gratin that I've seen before include "Dish covered with grated cheese" , "A dish cooked with grated cheese on it" , "'Au ..., with a cheesy topping (6)'" , "With a crisp, golden topping" , "Au . . . . . ., cooked with a covering of cheese" .)

I've seen this clue in The Independent.
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