Note hidden in cake is not in code (2,5)
I believe the answer is:
en clair
'not in code' is the definition.
(I've seen this before)
'note hidden in cake' is the wordplay.
'note' becomes 'n' (abbreviation).
'hidden in' means one lot of letters goes inside another.
'cake' becomes 'eclair' (I've seen this before).
'n' put into 'eclair' is 'EN CLAIR'.
'is' acts as a link.
(Other definitions for en clair that I've seen before include "Not using substitution, say" , "N ot in code/cipher" , "Not in cipher" , "Not in code or cypher" , "in ordinary language" .)