Fancy mash, Your Grace? (7)
I believe the answer is:
duchess
This clue is a double definition.
'fancy mash' is the first definition.
(French mashed potato dish)
'your grace?' is the second definition.
(Other definitions for duchess that I've seen before include "Noblewoman" , "Wife of a duke" , "Female aristocrat" , "Duke's wife" , "Noble lady" .)