Remove the skin from the onion and finely dice. Remove peel from potatoes, rinse and finely dice. Rinse apple thoroughly, cut into quarters and remove core. Cut apple into fine cubes. Remove a quarter of the apple cubes and sprinkle with juice of one lemon.
Heat oil in a saucepan, sauté onions, add potatoes and apple and also sauté briefly. Extinguish with clear soup and whipping cream, bring to the boil and simmer for about 20 minutes over medium heat with the lid closed. Add horseradish. Finely mash with a potato masher.
Season soup with salt, pepper and sugar. Rinse marjoram, shake dry and pluck leaves from stems. Serve soup in soup bowls. Serve with remaining apple cubes and marjoram leaves sprinkled on top.
Time needed : approx. 40 min.