Composer who made church music fashionable (6)
I believe the answer is:
chopin
'composer' is the definition.
(Frederic Chopin)
'made church music fashionable' is the wordplay.
'made church music' becomes 'chop' (I can't justify this - if you can you should believe this answer much more).
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'chop'+'in'='CHOPIN'
'who' acts as a link.
Can you help me to learn more?
(Other definitions for chopin that I've seen before include "Double centenarian" , "Composer of mainly piano works" , "No chip on this composer's shoulder" , "Romantic figure" , "See 10" .)