##Cover the potatoes and cook them in water for about 20 minutes. Cut ##beetroot## in half and cut into thin slices (Attention: dye strongly, best to wear disposable gloves!).
##peel onion## and cut into thin rings.
For the marinade, roast cumin in a pan without fat. Remove and crush finely in a mortar. Heat the oil in the pan. Sauté the onion in it. Add vinegar, 100 ml water and stock, bring to the boil, simmer for 2 minutes.
Season with salt, pepper, cumin, mustard and honey.
Drain, quench, peel and slice the potatoes. Pour hot marinade over potatoes and beetroot and mix everything carefully. Marinate for about 30 minutes.
Mix sour cream and horseradish. Season to taste with salt and pepper. Season potato salad again. Roll up roast beef and serve with dip and salad.