Den is after peach, oddly leaving cake (6)
I believe the answer is:
eclair
'cake' is the definition.
(I've seen this before)
'den is after peach oddly' is the wordplay.
'den' becomes 'lair' ('lair' can be a synonym of 'den').
'is after' is a charade indicator (letters next to each other).
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
The alternate letters of 'peach' are 'ec'.
'lair' put after 'ec' is 'ECLAIR'.
'leaving' is the link.
(Other definitions for eclair that I've seen before include "Bakery item" , "Chocolate-topped, cream-filled cake" , "teatime treat?" , "Finger-shaped, chocolate-iced, cream-filled cake" , "Food" .)