Peel the asparagus, cut off the woody ends. Wash the asparagus and cook in 3/4 litre of boiling salted water for 15-20 minutes. Drain and collect the stock. Skin and bone the eel.
Peel and finely chop the onions. Heat the fat in a pot and fry the onions until transparent. Fry the eel skin and bones. Dust with flour and deglaze with asparagus stock. Simmer for about 15 minutes at low heat.
Pour soup through a sieve. Whisk the egg yolks and four tablespoons of cream. Add remaining cream to the soup and bring to the boil. Cut asparagus and eel into pieces and add to the soup. Heat briefly and alloy with whisked egg yolk.
Do not let it boil anymore! Season to taste with salt, pepper, a pinch of sugar and some orange peel and garnish with dill flags.