Cake British composer eats when the news is on? (10)
I believe the answer is:
battenberg
'cake' is the definition.
(battenberg is a type of cake)
'british composer eats when the news is on?' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'composer' becomes 'berg' (20th Century Austrian composer).
'eats' indicates putting letters inside.
'when the news is' becomes 'at ten' (eg BBC 10 O'Clock News).
'on?' means one lot of letters goes inside another (as in clothing 'on' a person).
'berg' enclosing 'atten' is 'battenerg'.
'b' put inside 'battenerg' is 'BATTENBERG'.
(Another definition for battenberg that I've seen is " Marzipan-covered sponge cake".)