Wash, peel and dice the potatoes. Peel and chop the onions. Celery, carrots, parsley root peel, wash and also dice. Clean, wash and cut leek into rings.
Heat the oil in a pot. Fry the diced bacon and onion until transparent. Add potato and vegetable cubes and leek rings. Add vegetable stock and cook for about 10 minutes. Put 5 tablespoons of diced vegetables and bacon aside as a garnish.
Add the milk to the remaining vegetables, bring to the boil and puree finely with a hand blender. Bring the soup to the boil and remove from the stove. Mix egg yolk and sour cream. Alloy the soup with it. Add vegetable and bacon cubes to the soup.
Wash parsley, dab dry and cut into strips. Pour soup into a terrine and sprinkle with the parsley.