Boil potatoes and cut into slices. Cut radishes into wedges and onion into rings. Prepare lamb´s lettuce.
Marinade: Mix well vinegar and 2 tbsp. water, spice with salt and pepper. Add oil one after the other.
Cut beef into thin slices and cover with half of marinade for about 10 minutes. Put salad, potatoes, onion rings and radishes into a bowl, douse with the rest of marinade and blend carefully.