Restaurant serving fish topped in cheese (9)
I believe the answer is:
brasserie
'restaurant' is the definition.
(brasserie is a kind of restaurant)
'topped in cheese' is the wordplay.
'topped' becomes 'rasse' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'cheese' becomes 'brie' (Brie is an example).
'rasse' placed into 'brie' is 'BRASSERIE'.
'serving fish' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for brasserie that I've seen before include "Where to eat" , "eatery" , "eating place" , "bar serving food" , "Simple restaurant" .)