Murphy's treat, cooked (5)
I believe the answer is:
tater
'murphy's' is the definition.
(informal term for a potato)
'treat cooked' is the wordplay.
'cooked' is an anagram indicator (letters cooked into a new form).
'treat' with letters rearranged gives 'TATER'.
(Other definitions for tater that I've seen before include "Champ is mostly" , "Potato (informal)" , "Potato (colloq.)" , "found in vegetable basket" , "Murphy" .)