Prepare, as leftovers (6)
I believe the answer is:
reheat
'prepare as leftovers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for reheat that I've seen before include "Warm (food) up again" , "Method of getting extra power from jet engine" , "Bring back to the boil, for instance" , "Of cooked food, give another go in the microwave" , "Jet engine afterburner" .)