City den offers something sweet (6)
I believe the answer is:
eclair
'something sweet' is the definition.
(type of small cake)
'city den' is the wordplay.
'city' becomes 'EC' (the City of London postcode).
'den' becomes 'lair' (synonyms).
'ec'+'lair'='ECLAIR'
'offers' is the link.
(Other definitions for eclair that I've seen before include "Long chocolate cake for Claire" , "Bakery item" , "Type of cream cake" , "A long thin cake with chocolate covering" , "Long affair with pastry, chocolate and cream?" .)