Judge cooked rarebit (7)
I believe the answer is:
arbiter
'judge' is the definition.
(I've seen this in another clue)
'cooked rarebit' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'rarebit' with letters rearranged gives 'ARBITER'.
(Other definitions for arbiter that I've seen before include "Decision maker" , "Judge, adjudicator" , "Ref" , "One has the authority to settle disputes" , "Rarebit? (anag)" .)