Boil the chicken in about 3/4 of a litre salted water for about 30 min.Remove the meat to cool,set the stock aside.Mix the jogurt and egg yolk and fill into a pan with about half a litre of the stock mix well,stir all the time and reheat to just boiling point.Cut or rip the chicken into small pieces add to soup.Reheat just to boiling point.Season well with salt and pepper.