Top CIA agent initially mixed pudding (7)
I believe the answer is:
tapioca
'pudding' is the definition.
(tapioca pudding is a kind of pudding)
'top cia agent initially mixed' is the wordplay.
'initially' says to take the initial letters.
'mixed' indicates anagramming the letters.
The initial letter of 'agent' is 'a'.
'top'+'cia'+'a'='topciaa'
'topciaa' with letters rearranged gives 'TAPIOCA'.
(Other definitions for tapioca that I've seen before include "it thickens" , "Starchy pudding" , "Cassava product used for puddings" , "Substance from cassava used to thicken puddings" , "Ciao, Pat, have some strange pudding" .)