Fruit to put around a sort of cake (7)
I believe the answer is:
tangelo
'fruit' is the definition.
(I know that tangelo is an fruit)
'to put around a sort of cake' is the wordplay.
'put around' means one lot of letters goes inside another.
'a sort of cake' becomes 'angel'.
'to' going around 'angel' is 'TANGELO'.
(Other definitions for tangelo that I've seen before include "Citrus fruit hybrid" , "one cross, sour" , "sharp cross" , "Mixed fruit" , "Hybrid fruit; eat long (anag.)" .)