Sara.... have you tried making a prawn butter? Put some butter and cooked prawns into a food processor and whiz into a paste. Add some rock salt and a tbsp of vermouth and then heat in a pan and pour over a pan cooked fillet of cod.
It's just a cheapie I bought from the ferretería, Lamtaf.
Sara... the vermouth is optional but you could always add a table spoon of dry white wine. If the sauce looks like it is splitting, add a tiny bit of corn flour and keep stirring.