Boil potatoes until tender (30-40 minutes). Peel and cut in thin slices. In a large dish, put a layer of potatoes. Sprinkle with salt, pepper, sugar and some of the celery, onions and parsley. Sprinkle a little oil and vinegar over it. Repeat a layer of potatoes, etc. until all ingredients are used up. Grate the egg over the top and sprinkle with paprika. Garnish with sprigs of parsley.