Heat a frying pan until hot, add half the butter and fry the steak until just browned on each side then remove and set aside.
Add the remaining butter, turn the heat down slightly, then add the onion and fry until softened.
Add the mushrooms and fry until golden brown then add the brandy and flame to burn off the alcohol.
Stir in the tomato puree, smoked paprika and Dijon mustard and cook for 2 minutes.
Whisk in the beef stock and bring to the boil. Turn the heat down and simmer for 2 minutes then stir in the beef and sour cream and cook for another minute.
Season to taste then stir in half the parsley.
Heat the rice according to packet instructions, then stir in the rest of the parsley and serve with the stroganoff.