Clean the mushrooms, rinse and drain properly. Halve or quarter depending on size.
Peel and dice the onions.
Heat butter in a saucepan and sauté the onion until translucent. Add the porcini mushrooms and sauté briefly.
Heat the vegetable soup and pour it over the mushrooms. Cover and simmer at low temperature for about 10 minutes. Season to taste with salt and pepper.
Mix egg yolks with whipped cream. Mix with 3-4 tablespoons of hot soup and thicken the porcini mushroom soup with it.
Do not boil the porcini mushroom soup anymore, otherwise the egg yolk will flocculate.
Sprinkle with chopped parsley and serve hot!