Put the pork trotters in a deep pot, pour in water and put to boil, while removing the foam periodically. Take the boiled pork trotters out and leave them to cool slightly, then debone them well.
Put the broth in which you boiled the trotters on the stove again (you need about 8 1/3 cups (2 L) of it). After it reaches boiling point, add the meat from the trotters, black pepper, salt and 1 bay leaf.
Beat the yoghurt with the egg yolks and flour, pour in a little of the boiling broth, stir and pour it in a thin trickle slowly into the pot while stirring nonstop. Remove from the stove before it reaches boiling point.