Special ice cream cake (5)
I believe the answer is:
scone
'cake' is the definition.
(scone is a type of cake)
'special ice cream' is the wordplay.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'ice cream' becomes 'cone' (cone can refer to an ice cream cone).
's'+'cone'='SCONE'
(Other definitions for scone that I've seen before include "Cream tea cake" , "Savoury cake" , "ancient Scottish settlement" , "baked cake" , "Unsweetened cake" .)