Place salmon and cod in a deep container and cover with salted boiling water and a dash of white wine vinegar.
Remove cod after 20 minutes and salmon after 30 minutes, then warm briefly in a pan.
Flake the fish into a bowl and mix with mashed potato, onions, chillies, herbs, lemon juice, and zest.
Shape the mixture into 12 fishcakes and coat them in flour.
Fry the cakes in butter and oil for 6 to 8 minutes until golden on both sides.
Soak breadcrumbs in vinegar, then process with herbs, garlic, and seasoning into a coarse paste.
Slowly incorporate the olive oil into the processor with the motor running.
Add anchovies and capers and pulse for 2 seconds to retain texture.
Boil eggs for 3 minutes, peel while warm, stir yolks into the sauce, and fold in chopped whites.