Dainty piece of marzipan if left over (5)
I believe the answer is:
elfin
'dainty' is the definition.
(I've seen this before)
'piece of marzipan if left over' is the wordplay.
'piece of' says the answer is hidden in the clue.
'over' says the letters should be written backwards.
'nifle' can be found hidden inside 'marzipan if left'.
'nifle' back-to-front is 'ELFIN'.
(Other definitions for elfin that I've seen before include "Fairy-like" , "Dainty" , "Delicate, slight" , "Delicate little" , "Delicately framed" .)