Fish initially baked on some paper (5)
I believe the answer is:
bream
'fish' is the definition.
(type of fish)
'initially baked on some paper' is the wordplay.
'initially' indicates taking the first letters.
'on' is a charade indicator (letters next to each other).
'some paper' becomes 'ream' (a ream is an amount of paper).
The initial letter of 'baked' is 'b'.
'b'+'ream'='BREAM'
(Other definitions for bream that I've seen before include "Carp relative" , "Food fish" , "Broad, thin fish" , "Fish found in amber" , "Edible fish" .)