Seed on a bun (6)
I believe the answer is:
sesame
'seed on a bun' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sesame that I've seen before include "Plant yielding seeds used for flavouring bread" , "Oil plant from Ali Baba's cry" , "Seed or oil used in cooking" , "Seeds used for making oil" , "Open . . . . . . cries the magician" .)