Unexpected ingredient in his pudding (4)
I believe the answer is:
spud
'unexpected ingredient' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'in his pudding' is the wordplay.
'in' indicates a hidden word.
'SPUD' is hidden in the letters of 'his pudding'.
Can you help me to learn more?
(Other definitions for spud that I've seen before include "One could be in jacket" , "Spade; potato (slang)" , "King Edward, say (slang)" , "Starchy bit of food" , "Charlotte perhaps" .)