Paid in one go, say, for plump, sumptuous pudding ingredients (4,3)
I believe the answer is:
lump sum
'paid in one go say' is the definition.
The definition suggests a singular noun which matches the answer.
'plump sumptuous pudding ingredients' is the wordplay.
'ingredients' says the answer is hidden in the clue (certain parts or ingredients from the clue).
'LUMP SUM' is hidden in the letters of 'plump sumptuous pudding'.
'for' is the link.
Can you help me to learn more?
(Other definitions for lump sum that I've seen before include "Single payment as opposed to many instalments" , "Single amount of money" , "Amount of money paid all at once" , "Large single payment" , "Single cash payment" .)