Prepared, as prunes (6)
I believe the answer is:
stewed
'prepared as prunes' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stewed that I've seen before include "(Meat) simmered; (tea) over-infused" , "Was long embarrassed" , "was in agitated state" , "Cooked slowly" , "Slowly boiled" .)