Libertine seen around queen’s castle making cheese (9)
I believe the answer is:
roquefort
'cheese' is the definition.
(Roquefort is an example)
'libertine seen around queen's castle' is the wordplay.
'libertine' becomes 'roue' (roue is a kind of libertine).
'seen around' indicates putting letters inside.
'queen' becomes 'Q' (abbreviation for queen in chess).
'castle' becomes 'fort' (fort is a type of castle).
'roue' enclosing 'q' is 'roque'.
'roque'+'fort'='ROQUEFORT'
'making' acts as a link.
(Other definitions for roquefort that I've seen before include "French cheese - for torque (anag)" , "French blue-veined cheese" , "Soft blue ewe's cheese" , "French blue cheese" , "Cheese made from ewes' and goats' milk" .)