Banter over posh amateur producing book (6)
I believe the answer is:
joshua
'book' is the definition.
(I know that Joshua is a book)
'banter over posh amateur' is the wordplay.
'banter' becomes 'josh' (I've seen this in another clue).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'amateur' becomes 'a'.
'josh'+'u'+'a'='JOSHUA'
'producing' is the link.
(Other definitions for joshua that I've seen before include "Moses' successor who conquered Jericho" , "OT prophet" , "OT book" , "Judges found next to this" , "The -- Tree, U2 album; successor to Moses" .)