Dainty milk supplier pens Italian book (6)
I believe the answer is:
titbit
'dainty' is the definition.
(titbit is a kind of dainty)
'milk supplier pens italian book' is the wordplay.
'milk supplier' becomes 'tit'.
'pens' indicates putting letters inside.
'italian' becomes 'it'.
'book' becomes 'b'.
'it'+'b'='itb'
'tit' enclosing 'itb' is 'TITBIT'.
(Other definitions for titbit that I've seen before include "Choice bit of something, food or gossip" , "Small item of gossip" , "Small tasty morsel" , "Small tasty bit of food" , "Small piece of tasty food" .)