Heat the lard. Chop the onions, carrots and the leek and fry in them. Dust with flour and fry briefly. Then add the meat stock and simmer for a quarter of an hour.
Now peel the potatoes, cut into small cubes and cook for another twenty minutes.
Remove the saucepan from the heat, whisk the cream with the egg yolks and mix into the soup. Sprinkle the whole with the chopped parsley or the chervil.