Clean and wash spring onions and cut into fine rings. Clean, wash and finely slice mushrooms and porcini
Heat 2 tablespoons of fat in a saucepan. Sauté spring onions in it. Add mushrooms and steam. Season with salt and pepper. Add 3/4 l water and cream. Bring to the boil, stir in broth and simmer for about 15 minutes
In the meantime, knead the flour and 1 tablespoon of butter, chill briefly if necessary. Season soup with salt, pepper and sherry. Stir flour butter into the soup in small pieces to bind it. Arrange and garnish with chervil