Wash the potatoes and boil in water for about 25 minutes. Drain and peel. In the meantime, stir yoghurt and crème légère until smooth, season with salt and pepper. Clean and wash spring onions and cut them into diagonal slices. Peel and finely grate the carrot.
Wash the apple and grate it coarsely. Mix immediately with lemon juice. Mix vegetables and apple with the yoghurt cream. Cut the maties into diagonal slices and serve with boiled potatoes and yoghurt dip. Garnish as desired with chervil and apple slices