Bran muffin topping (4)
I believe the answer is:
oats
'bran muffin topping' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oats that I've seen before include "Cereal for porridge" , "Food for horses and Scots (said Dr Johnson)" , "Porridge ingredient" , "Grains or porridge" , "A cereal crop" .)