A fortune? The sauce! (4)
I believe the answer is:
mint
This clue might be a double definition.
'a fortune?' is the first definition.
(making a mint is making a lot of money)
'sauce' is the second definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'the' is the link.
Can you help me to learn more?
(Other definitions for mint that I've seen before include "Building where coin money is made (4)" , "Sweet - in perfect condition" , "sweet herb" , "Make coin - herb" , "Large sum of money" .)