Wash the half chicken well and divide it into 2-3 pieces, cut the onion in half. In a large pot put 2 liters of cold water. Add chicken pieces, veal and pork shoulder, vegetables and greens. Add all spices as well as aromatics, bring to a boil and simmer until meat is tender. Strain soup and chill so that fat can then be skimmed off. Meanwhile, remove the chicken and cut into bite-sized pieces, as well as the veal and pork. Cut vegetables into small cubes. Bring the degreased soup back to the boil. Mix sour cream with flour and egg yolks until smooth. Add to soup while stirring briskly with a whisk and season with salt. Add meat and vegetable cubes again and reheat, but do not boil anymore. Sprinkle with chopped chives or parsley and serve in warmed soup plates.