Retired master, single, making dish from leftovers (7)
I believe the answer is:
rissole
'dish from leftovers' is the definition.
'retired master single' is the wordplay.
'retired' shows that the letters should be reversed in order.
'master' becomes 'sir'.
'single' becomes 'sole' ('sole' can be a synonym of 'single'**).
'sir' written backwards gives 'ris'.
'ris'+'sole'='RISSOLE'
'making' is the link.
(Other definitions for rissole that I've seen before include "Fried small cake of chopped meat" , "Sil rose for the meatball" , "faggot" , "Compressed meat and spices in breadcrumbs, fried" , "Minced meat or fish deep fried in egg and breadcrumbs" .)