Sinks part of Cornetto into pancake (4,5)
I believe the answer is:
drop scone
'pancake' is the definition.
(another name for a Scotch pancake)
'sinks part of cornetto' is the wordplay.
'sinks' becomes 'drops' ('drop' can be a synonym of 'sink').
'part of cornetto' becomes 'cone' (ice cream cone).
'drops'+'cone'='DROP-SCONE'
'into' acts as a link.
(Other definitions for drop scone that I've seen before include "Small and thick pancake" , "Girdlecake" , "Scotch pancake" , "cake" , "Eating" .)