Latte topping (4)
I believe the answer is:
foam
'latte topping' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for foam that I've seen before include "Boiling bubbles" , "Froth created by wave or soap" , "Froth or spume" , "Bubbles on liquid" , "Sea froth" .)