Cooked too long (8)
I believe the answer is:
overdone
'cooked too long' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for overdone that I've seen before include "Hammed up" , "Cooked too much or carried too far" , "Cooked too long" , "Exaggerated; burnt (meat)" , "Exaggerated - far from rare" .)