Vichyssoise garnish (6)
I believe the answer is:
chives
'vichyssoise garnish' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for chives that I've seen before include "Herb of the onion family" , "Plant of onion family" , "Herbs with long tubular onionflavoured leaves" , "Plants" , "Leaves used as onion-flavoured seasoning" .)