Wash, dry and cut the chicken breast fillet into strips. Let the oil get hot in a pan and then fry the meat in it and then keep it warm. Cut the potatoes into small cubes. Cut the onion into rings. Briefly sauté the potatoes in the frying fat. Pour in water and bring to the boil, add the chicken stock. Let the soup boil over medium heat. Clean and wash the rocket, remove the stalks, add to the soup and puree everything. Season with pepper and season to taste. Add the meat and let it get hot in the soup. Stir in the sour cream.