Cook the jacket potatoes for approx. 20 minutes until soft. Remove the peel and refrigerate.
Mix the sour cream, yogurt, mustard, horseradish, dill and parsley. Fold in the cucumber, carrots, apple, onion and bell pepper. Halve the tomato and eggs, cut into slices and mix in. Season to taste with salt, pepper and sugar.
Cut the cold potatoes into thin slices and fold in. Let it soak for at least 2 hours, even better overnight.