Slice the onion and apple; fry them in the butter, and then rub them through a hair sieve.
Mix the flour and curry powder smoothly with the stock.
Stir over the fire and boil well.
Then add the onion, apple, lemon juice, and salt.
Break the fish into pieces, and remove the bones.
Put it into the sauce, and let it warm through.
Serve with a border of rice round it.