Chef's sauce ingredient (4)
I believe the answer is:
roux
This clue could be a double definition.
'chef's sauce' is the first definition.
'roux' can be an answer for 'sauce' (I've seen this before). I'm not certain of the 'chef's' bit.
'ingredient' is the second definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
Can you help me to learn more?
(Other definitions for roux that I've seen before include "Fat and flour mixture, cooked and used to make sauces" , "Butter and flour sauce combination" , "Mixture of fat and flour used for thickening sauces" , "Thickener for sauces" , "Fat/flour sauce-mix" .)