Pudding made by son in the past (4)
I believe the answer is:
sago
'pudding' is the definition.
(I've seen this before)
'by son in the past' is the wordplay.
'by' says to put letters next to each other.
'son' becomes 's' (genealogical abbreviation for son).
'in the past' becomes 'ago' (synonyms).
's'+'ago' is 'SAGO'.
'made' acts as a link.
(Other definitions for sago that I've seen before include "Starchy foodstuff" , "Cereal, used in pudding" , "Edible powdery starch" , "Palm cereal" , "Starchy cereal used in puddings" .)