Thick soup cowherd prepared (7)
I believe the answer is:
chowder
'thick soup' is the definition.
(type of soup)
'cowherd prepared' is the wordplay.
'prepared' is an anagram indicator.
'cowherd' is an anagram of 'CHOWDER'.
(Other definitions for chowder that I've seen before include "Fish soup for cowherd" , "Thick seafood soup" , "Thick fish stew" , "Rich soup with fish, clams etc." , "Clam stew, soup" .)