Pluck the parsley leaves from the stems. Peel the potatoes and cut into pieces.
Cook the potato pieces in a saucepan with half of the parsley, vegetable stock and spices until the potatoes are tender.
In the meantime, cut the mushrooms into small pieces and slowly fry them in butter in a pan.
When the potatoes are soft, stir the soup with the hand blender until frothy. Just before the end of the pureeing process, add the other half of the parsley leaves and puree. You can still see a few more leaves in the soup.
Arrange the soup in deep plates or bowls and finally add the fried mushrooms.