A gem of a loaf (8)
I believe the answer is:
baguette
I believe this is a double definition.
'a gem' is the first definition.
(I've seen this in another clue)
'a loaf' is the second definition.
(baguette is a kind of loaf)
'of' is the link.
(Other definitions for baguette that I've seen before include "Long loaf - tube gate (anag)" , "A long thin French loaf" , "Get beaut of a French loaf" , "Bread roll" , "Long French breadstick" .)