Biscuit, e.g. turning rotten (6,3)
I believe the answer is:
ginger nut
'biscuit' is the definition.
(type of biscuit)
'e g turning rotten' is the wordplay.
'rotten' indicates anagramming the letters.
'e'+'g'+'turning'='egturning'
'egturning' with letters rearranged gives 'GINGER-NUT'.
(Other definitions for ginger nut that I've seen before include "Type of biscuit" , "Kind of biscuit" , "Variety of biscuit" , "redhead?" , "Spicy biscuit" .)