Clean and wash the mushrooms, then put half of them through a meat grinder. Saute them on low heat along with the rest of the sliced mushrooms and grated onion for about 10 minutes.
Fry with the flour, then add the broth and black pepper. Take the soup off the fire, thicken it with the cream whipped with the eggs and sprinkle it with finely chopped parsley.
Return to the stove and boil for a bit longer.