What's used to sweeten pudding courses when processed (7)
I believe the answer is:
sucrose
'what's used to sweeten pudding' is the definition.
'courses when processed' is the wordplay.
'when processed' is an anagram indicator.
'courses' anagrammed gives 'SUCROSE'.
(Other definitions for sucrose that I've seen before include "Sweet compound" , "Main part of cane sugar" , "Something in nectar" , "Sweetening agent -- Croesus (anag)" , "Chief component of cane or beet sugar" .)