Mushrooms are cleaned and cut into slices, fried to golden in half the amount butter, removed in dish. In a saucepan, onion cut in crescents fry in remaining butter (can add a little olive oil if onion is plenty) until slightly caramelized of the natural sugars in it, put the flour and stir vigorously to spread everywhere. Add broth and bring to the boil put spices (salt, thyme, white pepper) and water as needed. Once the onion is tender and ready to be broken down separately yolk and cream and add to the soup. Finally, put the mushrooms and soup simmer for a few minutes to blend flavors. Season with lemon juice optional. * This idea is inspired by the French onion soup and without claim to authorship.