Type of cake that's a hit (5)
I believe the answer is:
pound
This clue is a double definition.
'type of cake' is the first definition.
'a hit' is the second definition.
(I know that pound is a more specific form of hit)
'that's' acts as a link.
(Other definitions for pound that I've seen before include "Batter" , "UK currency; weight" , "Money - belt" , "Lay on, money" , "place of confinement" .)