You'll get mostly bananas in cake (4,3)
I believe the answer is:
yule log
'cake' is the definition.
(I have seen 'Seasonal cake ' mean 'yule log' so perhaps 'cake' could also mean 'yule log')
'you'll get mostly bananas' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'bananas' is an anagram indicator (bananas can informally mean crazy).
'youll'+'get'='youllget'
'youllget' with its final letter taken off is 'youllge'.
'youllge' with letters rearranged gives 'YULE-LOG'.
'in' is the link.
(Other definitions for yule log that I've seen before include "Christmas chocolate cake" , "Xmas chocolate cake" , "Chunk of wood for the Christmas fire" , "fuel for seasonal fire" , "Christmas fuel" .)