Pureed nut boxed by a customer (6)
I believe the answer is:
punter
'a customer' is the definition.
(I've seen this before)
'pureed nut boxed by' is the wordplay.
I cannot quite see how this works, but
an anagram of 'nut' is 'unt' which is present in the answer.
'by' could be 'per' (I've seen this in another clue) and 'per' is located in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for punter that I've seen before include "boater" , "Gambler; customer" , "Person who bets" , "A colloquial better or a regular client" , "Better - rugby player - river boatman" .)