Wash and peel the white asparagus (500 g). Cut off the woody ends. Then put the peel and the cut ends into about 1.5 litres of boiling water. After 20 minutes of simmering, take off ends and peel out of the water with a ladle and throw them away. Keep the asparagus stock and add some salt and a pinch of sugar.
Cut the actual asparagus spears into pieces about 3 cm long and put them into the broth to cook for about 15 minutes until tender. Then lift the asparagus pieces out of the broth and put them aside in a bowl.
Heat 50 g of butter in a saucepan and add the flour (50 g), stirring constantly. Then slowly pour in the asparagus stock, add two tablespoons of white wine and let everything boil for another 10 minutes until it becomes a creamy soup. Now take the pot off the cooker.
Whisk the cream with the egg yolk and slowly add it to the asparagus soup. Do not bring the cream of asparagus soup to the boil! Then season to your taste with salt and pepper. If necessary, you can also add a dash of lemon juice to taste.
Now you just have to add the asparagus pieces to the soup and voilà, the soup is ready to serve. For garnish, a few croutons and scattered herbs (especially chervil or cress) look good and make the soup even more visually appealing.