To prepare the beef, pat it dry, and cut it into 1 cm x 5 cm strips. Place the beef, 1 tablespoon of Stroganoff blend and the flour into a bowl and mix until the beef is coated. If the meat is sticking together, add a little more flour.
In a large frying pan, heat half the butter and half the olive oil. Fry the beef over high heat in small batches until browned. Remove the beef from the pan and set aside. Add the onion and mushrooms to the pan along with the rest of the butter and oil and sauté over medium heat for 5 minutes. Add the white wine and stir to deglaze the pan. Continue cooking until the wine has almost evaporated.
In a bowl, whisk together the cream, stock, remaining spice blend, mustard, salt and lemon juice until smooth. Add this to the pan along with the beef and cook for approximately 5 minutes, stirring occasionally. The flour from the beef coating will thicken the sauce. If it is still too runny, mix 1 tablespoon of cornflour with a little cold water and add a little at a time, stirring it through the mixture until the desired consistency is reached.
Remove from the heat and add the additional butter and the parsley. Mix through until the butter has melted. Serve straight away with mashed potatoes or pasta.
