Peel the carrots and celery and coarsely grate them in a food processor or with a vegetable slicer. Clean the leek or spring onions and cut into fine rings. Mix everything together.
Mix the sweet cream, yoghurt, mayonnaise and lemon juice in a bowl and season with salt. Pour over the salad and mix well. Cover and let steep in the refrigerator for at least 1 hour.
Take out 15 minutes before serving and sprinkle some smooth, chopped parsley on top.