Sweat the shallots in the butter with a pinch of salt for 3 minutes. Do not let them colour.
Add the mushrooms and continue to sweat for 5 minutes.
Now add the water and chicken stock (replace the chicken stock with water for vegetarians).
Bring to the boil and reduce to a simmer. Cook out for 20 minutes.
sauté the garnish mushrooms and hazelnuts in butter while the soup is simmering.
After 20 minutes, pour the soup into a liquidiser and blend until smooth. Place in a saucepan and using a hand blender whisk in the remaining butter. Correct the seasoning and serve garnished with the sautéed mushrooms and hazelnuts.