Unusual ingredient in his pudding (4)
I believe the answer is:
spud
'unusual ingredient' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'in his pudding' is the wordplay.
'in' indicates a hidden word.
'SPUD' can be found hidden inside 'his pudding'.
Can you help me to learn more?
(Other definitions for spud that I've seen before include "Potato (informal)" , "Starchy bit of food" , "Charlotte perhaps" , "Tattie" , "Spade; potato (slang)" .)