Preparing a vinaigrette? (8)
I believe the answer is:
dressing
This clue is a double definition.
'preparing' is the first definition.
(dressing is a kind of preparing)
'a vinaigrette?' is the second definition.
(vinaigrette is a kind of dressing)
(Other definitions for dressing that I've seen before include "Mustard" , "Sauce for salads" , "but not stripping!" , "French or vinaigrette, say" , "Sauce - alignment - bandage" .)