Epicure curses onion in the soup (11)
I believe the answer is:
connoisseur
'epicure' is the definition.
(thesaurus)
'curses onion in the soup' is the wordplay.
'in the soup' indicates anagramming the letters (soup can mean a mixture).
'curses'+'onion'='cursesonion'
'cursesonion' is an anagram of 'CONNOISSEUR'.
(Other definitions for connoisseur that I've seen before include "discriminating judge" , "Knowledgeable art-lover" , "Expert judge of taste" .)