Cake mix need (3)
I believe the answer is:
egg
'cake mix need' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for egg that I've seen before include "The advertising slogan exhorted us to go to work on one" , "Reproductive unit" , "Food in a shell" , "Early stage of development" , "On the face, it's embarrassing" .)