Sauce lost when cooking stew (9)
I believe the answer is:
cassoulet
'stew' is the definition.
(I know that cassoulet is a type of stew)
'sauce lost when cooking' is the wordplay.
'when cooking' is an anagram indicator (letters cooked up into a new form).
'sauce'+'lost'='saucelost'
'saucelost' anagrammed gives 'CASSOULET'.
(Other definitions for cassoulet that I've seen before include "French stew made with meat and beans" , "dish" .)