Poach the fish in Court Bouillon for 15 minutes.
Skin and bone it, mash up the fish carefully, mixing with the bread previously soaked in milk and pressed out again.
Add the puree of potatoes, season, bind with yolk of egg, a whole egg, and then a white of egg beaten very stiff.
The paste should be smooth and soft.
Roll it out on a floured board.
Cut out your dumplings from it, and cook them for about 10 minutes in salted boiling water.
A word of advice: always try, first, to cook just one dumpling, so that if the paste is too soft you can make it firmer with more bread, fine breadcrumbs or flour. serve as desired.