Finely chop the onion and fry in a frying pan with oil until golden brown. Then let cool.
Grind the fish fillet in a blender, add 1 raw yolk and mix well. Add the onion, breadcrumbs, salt and pepper. Mix.
Spread out some cling film and place the minced meat in a convenient form for rolling into a roll.
Cut the boiled eggs into small pieces and place on top of the minced meat.
Roll into a roll, brush with the remaining yolk, sprinkle with the remaining breadcrumbs and place in a preheated oven at 180 °C for 1 hour.