Wash and peel the asparagus and generously cut off the woody ends. Asparagus peel and ends, boil 1 1⁄4 l water, salt and 1 pinch of sugar. Simmer for about 10 minutes, then drain and collect the asparagus stock in a pot.
Cut the asparagus spears into pieces. Bring the asparagus stock back to the boil, cover and cook the asparagus pieces for about 10 minutes. Pour off the water and collect 1 l asparagus stock.
Peel and chop the onion. Heat 30 g butter. Sauté onion in it. Sprinkle with flour and sauté. Add asparagus stock and cream while stirring, bring to the boil and simmer for about 5 minutes.
Cut the bread into small cubes. Roast in 2-3 tablespoons of hot butter. Wash dill and chop finely. Warm asparagus and prawns briefly in the soup. Whisk the egg yolks. Mix 6 tbsp. of soup with the egg yolks bit by bit.
Remove the soup from the stove, stir the egg yolks into the soup (must not boil any more!). Season with salt, pepper, 1 pinch of sugar and Noilly Prat. Sprinkle with croutons and dill.