Dairy product beating the very best (8,5)
I believe the answer is:
whipping cream
'dairy product' is the definition.
(whipping cream is a kind of dairy product)
'beating the very best' is the wordplay.
'beating' becomes 'whipping' (synonyms).
'the very best' becomes 'cream' (as in the cream of the crop).
'whipping'+'cream'='WHIPPING-CREAM'
(Other definitions for whipping cream that I've seen before include "Beat it" , "It needs to be stiffened" , "food" .)