Soften the potatoes with the peel, peel and cut into small leaves. Harden the egg, peel it, remove the yolks, mash them finely with a fork, stir with mustard.
Add oil drop by drop at the beginning, later stir in fine thread to make a mayo. Season to taste with the juice of a lemon, salt and freshly ground pepper. Cut herrings into bite-sized pieces, dice cooked beet. Cut gherkin into slices.
Peel apple, cut into quarters, remove core, cut into slices. Mix all ingredients into the leaf salad. Mix well.