Cornmeal mush (7)
I believe the answer is:
'cornmeal mush' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for polenta that I've seen before include "Italian porridge usually of maize" , "Italian boiled cornmeal" , "Cooked meal" , "Lepanto (anag.)" , "Italian maize dough" .)