Soak herring fillets in milk, then pass them along with white bread and onion through a meat grinder twice.
Soften the butter, then mash the hard-boiled egg yolks with mustard and pepper.
Mix everything thoroughly.
Ingredients: 60g herring fillet, 60g white bread, 60g milk, 60g butter, 1 onion, 1 egg, mustard, pepper.