Bird atop cheese (7)
I believe the answer is:
stilton
'cheese' is the definition.
(stilton is a cheese)
'bird atop' is the wordplay.
'bird' becomes 'stilt' (stilt is a kind of bird).
'atop' becomes 'on' ().
'stilt'+'on'='STILTON'
(Other definitions for stilton that I've seen before include "Cheese named after Cambridgeshire town" , "Strong Eng. cheese" , "Strong English cheese, originally from Leicestershire" , "English cheese, usually veined" , "rich food?" .)