Poach the fish in the milk for 5 to 7 minutes. Flake the fish, fry the finely chopped onion in butter until translucent.
Combine the fish, mashed potatoes, onion,, chopped parsley and chopped capers, add salt and pepper.
Shape into cakes, roll in flour, dip into beaten egg and roll in breadcrumbs. Fry in butter or grill.