A bit tart with chef, oddly (5)
I believe the answer is:
piece
'a bit' is the definition.
('piece' can be a synonym of 'bit')
'tart with chef oddly' is the wordplay.
'tart' becomes 'pie' (I've seen this before).
'with' means one lot of letters go next to another.
'oddly' means one should take alternating letters.
The alternate letters of 'chef' are 'ce'.
'pie'+'ce'='PIECE'
(Other definitions for piece that I've seen before include "Musical composition" , "Section; firearm" , "man on board" , "Separate part of a whole" , "Chessman; portion" .)