Peel the onion and carrots. Wash tomatoes. Chop everything up roughly. Wash the meat and bring to the boil with onion, carrot, tomatoes, peppercorns, marjoram and 1.5 liters of water. Cover and simmer over low heat for 35-40 minutes.
Peel, wash and finely chop the potatoes and the rest of the carrots. Sauté in hot oil in a saucepan. Season with salt and pepper. Lift the meat out of the broth, allow to cool a little. Pour the stock into the potatoes through a sieve. Bring to the boil and simmer for about 20 minutes.
Cut the chicken breast into strips. Wash the chives and cut finely, except for some of them. Lift 1/3 vegetables out of the broth and finely dice. Finely mash or puree the rest of the vegetables in the broth. Heat the meat and diced vegetables in the soup. Season to taste with salt and pepper. Serve with sour cream and chives.