Heat the oil in a large pan, tip in the onions and cook for 10 mins until soft and golden. Add the pork and mushrooms and cook on a high heat for 3-4 mins until browned. Add the paprika and cook for 1 min more.
Stir in the tomato purée, then pour on the stock and simmer for 5-8 mins until the pork is cooked through. Finally, mix in the soured cream and some seasoning. Serve with egg noodles, tagliatelle or rice, and an extra dollop of soured cream, if you like.