Mix together the paprika and flour in a large bowl, add the beef and turn to coat.
Cook the rice in lightly salted boiling water for 13 minutes until cooked but firm. Drain, set aside and keep warm.
Meanwhile, melt the butter and 2 tablespoons of the oil in a large frying pan and cook the onion for about 6 minutes or until soft. Add the mushrooms and cook for a further 5 minutes or until soft. Remove with a slotted spoon and set aside.
Add the remaining oil to the pan, increase the heat to high and add the beef. Fry until browned all over, then reduce the heat. Return the onion mixture to the pan along with the soured cream; bring to the boil, then reduce the heat and allow to bubble gently for 1–2 minutes. Season well.
Serve immediately with the cooked rice and a sprinkling of chopped parsley.