Peel the asparagus, cut off the woody ends. Wash asparagus shells and put them in 800 ml boiling water. Season with salt, sugar and lemon slice. Let it simmer at medium heat for about 20 minutes. In the meantime, cut the asparagus into very fine pieces. Pour the asparagus peelings onto a sieve, collect the stock, bring to the boil again. Cook the asparagus in this stock for about 5 minutes.
Pour through a sieve, collecting the vegetable water. Heat the fat in a saucepan and sauté the flour in it. Add the vegetable water and 150 g whipped cream, stirring constantly, bring to the boil. Season to taste with salt and pepper. Whisk 50 g cream and egg yolk, stir into the soup. (Do not let it boil any more!) Add vegetables. Leave bacon in a pan without fat until crispy and add to the soup. Garnish soup with basil leaves