Rhubarb cake (6)
I believe the answer is:
waffle
This clue could be a double definition.
'rhubarb' is the first definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'cake' is the second definition.
(I know that Waffle is a type of cake)
Can you help me to learn more?
(Other definitions for waffle that I've seen before include "Trivial talk; cake" , "an iron product" , "something for breakfast" , "Batter-cake; vacillate" , "blather" .)