Initially, chef's assistant on board cooked stew (9)
I believe the answer is:
carbonado
'stew' is the definition.
(historical term for a type of stew)
'initially chef's assistant on board cooked' is the wordplay.
'initially' indicates taking the first letters.
'cooked' is an anagram indicator.
The first letters of 'chefs assistant' is 'ca'.
'on'+'board'='onboard'
'onboard' with letters rearranged gives 'rbonado'.
'ca'+'rbonado'='CARBONADO'
(Other definitions for carbonado that I've seen before include "Beef stew; black diamond" , "Meat grilled" , "Dark diamond used in industry for drilling and polishing" .)