How to cook
Finely chop the onions and mushrooms into crescents. Mix together the butter and olive oil, heat them and use them to stew the vegetables (onions and mushrooms).
Let the soup boil on low heat under a lid for 25-30 min. Mix the cream with 1 cup of the soup, to equalize the temperature, then add it to the mushrooms.
Boil for 5 minutes.