Dessert pudding (7)
I believe the answer is:
tapioca
I believe this is a double definition.
'dessert' is the first definition.
(I've seen this before)
'pudding' is the second definition.
(tapioca pudding is a kind of pudding)
(Other definitions for tapioca that I've seen before include "I act OAP (anag) - edible substance made from cassava" , "Starch from cassava used in making puddings" , "it thickens" , "Pudding made from an extract of cassava" , "Foodstuff used as a thickener" .)