Mashed pear in cold cheese (10)
I believe the answer is:
caerphilly
'cheese' is the definition.
(thesaurus)
'mashed pear in cold' is the wordplay.
'mashed' indicates an anagram.
'in' indicates putting letters inside.
'cold' becomes 'chilly' (I've seen this before).
'pear' anagrammed gives 'aerp'.
'aerp' placed inside 'chilly' is 'CAERPHILLY'.
(Other definitions for caerphilly that I've seen before include "Mild white cheese" , "Welsh town" , "Town north of Cardiff" .)