Ravels composition on a tray (6)
I believe the answer is:
salver
'tray' is the definition.
(I know that salver is a type of tray)
'ravels composition' is the wordplay.
'composition' indicates an anagram.
'ravels' anagrammed gives 'SALVER'.
'on a' is the link.
(Other definitions for salver that I've seen before include "Presentation tray" , "A posh silver tray" , "A tray on which something is presented" , "Tray, sometimes silver" , "A fancy metal tray" .)