Melt the butter in a saucepan.
The pan should not be taken very small, so that during cooking it will not be replaced with a larger one, since it will have to pour the broth into it.
In a saucepan heated with butter, fry finely chopped onions.
Add finely chopped mushrooms and continue frying for another 5 minutes.
Mixing directly on the stove in the pan add flour.
Pour the chicken stock after the flour. While mixing, bring the soup to a boil.
Once the broth boils, add parsley and celery.
All this must be cooked for 45 minutes on low heat.
Next, listen to the parsley and celery from the pan, and pour the broth into other dishes.
According to the recipe, the solid components of the soup must be passed through a sieve, however, the recipe is old and it was visible at that time there were still no mixers and food processors, so we chopped it all with a blender.
The result is a mixture, as in the photo.
Mushroom-onion mass will have to be mixed again with the broth.
Leave the broth alone and with a whisk, beat the yolks with cream.
With a thin stream, stirring, add whipped cream and yolks to the hot soup.
Again we put the pan with mushroom soup on the fire.
While stirring, heat the soup puree but do not bring to a boil.
It remains only to salt to taste and serve with croutons.