Clean the asparagus and spring onions and cut into small pieces. Cook in the broth for about 15 minutes. Puree half of the vegetables in a mixing bowl with the sour cream and parsley, put back in the saucepan and bring to the boil again.
If necessary tie with roux (does not have to be, only if you prefer tied soups). Fold in the egg yolks, but don`t let them boil anymore. Season to taste with the spices.