1. For the broth, in a pot, add the onion, carrot, celery, herbs, mushroom stems, pour in the water, and simmer for 20 minutes with the lid on.
2. Melt 50 grams of butter in a saucepan, add finely chopped onion and fry for about 10 minutes on a slow fire until softened.
3. Add the flour, stir and fry for 2-3 minutes, then gradually add the hot broth, stirring continuously.
4. Add half of the mushrooms and cook for 20 minutes, then strain the soup through a sieve.
5. Melt the remaining butter in a pan, squeeze the lemon juice, add the remaining mushrooms, season with salt and pepper to taste, and cook for 15 minutes.
6. Put the soup back in the pot, add the sautéed mushrooms, bring to a simmer over low heat.
7. Mix the cream together with the egg yolks and pour in a thin stream, stirring continuously until thickened (DO NOT BOIL).
8. Serve the soup with fried mushrooms, oil, and greens.
