Corner slice of macaroni cheese (5)
I believe the answer is:
niche
'corner' is the definition.
(I know that corner can be written as niche)
'slice of macaroni cheese' is the wordplay.
'slice of' indicates a hidden word.
'NICHE' is hidden within 'macaroni cheese'.
(Other definitions for niche that I've seen before include "A small recess or easy job" , "ideal position" , "Nook or recess" , "Suitable location" , "somewhere comfortable" .)