Rinse the trotters. Add trotters and water to cover in a pot, preferably a pressure cooker. Cook until the meat starts to come off the bones easily.
Drain the water into another pot, to get rid of any small bones. Used a wire colander.
Separate all the meat and the marrow from the bones and cut into small pieces. Add these back to the drained water.
In a separate bowl mix well all the thickening ingredients until you obtain a smooth mixture.
Add several spoons of the soup to the thickening mixture, one by one, while stirring the thickening mixture. Once this mixture is warm pour it slowly into the soup, again while mixing the soup. If you do not make the thickening mixture warm or you do not stir the yogurt and/or the egg will be cooked too fast and will have an unpleasant look in the soup.
Heat the soup to boil one last time and remove it from heat.
Taste and add salt if necessary.
Serve warm with the garnish served in individual bowls.