Crusty loaf (7)
I believe the answer is:
bloomer
'crusty loaf' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for bloomer that I've seen before include "A loaf; an error" , "A slangy blunder or flower in blossom" , "Stupid error (colloq.)" , "rose, say" , "Big mistake" .)