Wash the potatoes and cook in boiling water for about 20 minutes. In the meantime, wash the marjoram, shake dry and roughly chop the leaves of 3 stalks. Finely dice the gherkins. Mix mayonnaise, gherkins, 1 tbsp. cucumber stock, chopped marjoram and horseradish and season to taste with salt and pepper.
Clean and clean the mushrooms and cut them into thick slices. Wash and clean spring onions and cut them diagonally into thin rings. Drain the potatoes, rinse briefly in cold water and peel. Cut potatoes into slices.
Heat clarified butter in a large, coated pan. Fry the potatoes for about 10 minutes while turning. Season with salt and pepper. Finally add spring onions. Arrange the fried potatoes, 5 slices of roast beef and horseradish romoulade each and sprinkle with marjoram and coarse black pepper.