Season the beef and shape into walnut-sized meatballs. Heat the oil in a pan and cook the meatballs until brown on all sides. Scoop out of the pan and set aside. Add the onion to the pan and cook for a few mins to soften. Add the garlic and mushrooms, and fry for a few mins until the mushrooms soften and start to brown a little. Stir in the tomato purée, paprika and flour for 1 min, then add the stock, bit by bit, to make a smooth sauce. Return the meatballs to the pan, cover and simmer gently for 15 mins or until the meatballs are cooked through.
Stir in the soured cream and most of the parsley, and season to taste. Serve scattered with the remaining parsley, with rice, mashed potato or tagliatelle.