A peach in mustard, perhaps? (3,5)
I believe the answer is:
hot stuff
'a peach' is the definition.
(both can mean an attractive person)
I don't understand how the remainder of the clue works.
(Other definitions for hot stuff that I've seen before include "Dish" , "Recently stolen items" , "Such a talented person" , "Exciting thing" , "latest gear" .)