Brute cooked a potato (5)
I believe the answer is:
tuber
'a potato' is the definition.
(potato is an example of a tuber)
'brute cooked' is the wordplay.
'cooked' is an anagram indicator (letters cooked into a new form).
'brute' with letters rearranged gives 'TUBER'.
(Other definitions for tuber that I've seen before include "Underground stem, root" , "Fleshy root, vegetable say" , "or still vegetating?" , "Potato, for example" , "One goes underground" .)