Worthless pudding (4)
I believe the answer is:
duff
I believe this clue is a double definition.
'worthless' is the first definition.
(I've seen this before)
'pudding' is the second definition.
(I know that Duff is a type of pudding)
(Other definitions for duff that I've seen before include "Useless -- broken" , "Heavy pudding - no good" , "Dud - pud" , "Worthless; pudding" , "Heavy boiled or steamed pudding" .)