Peel, wash and thinly slice the potatoes. Peel and chop the onion. Heat 2 tablespoons of oil in a wide saucepan, fry the onion in it. Add 400 ml water, bring to the boil, stir in broth. Cover the potatoes and cook for 8-10 minutes.
Form the mince into 8 meatballs. Fry in 2 tablespoons of hot oil in a pan for about 8 minutes.
In the meantime, clean, wash and slice the radishes. Cucumber wash, clean, cut into slices. Season potatoes with salt, pepper and vinegar. Add the radishes and cucumber and let it steep for a short time. Stir in sour cream. Sprinkle ragout with cress as desired, eat with the meatballs.