Sweet cake topping (5)
I believe the answer is:
icing
'sweet cake topping' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for icing that I've seen before include "Top cake layer" , "Maybe Madeira's topping" , "that finishes off 29 [ANGEL CAKE]" , "Showing effect of cold snap" , "causes trouble at airports?" .)