Sprinkle the seasoning mix on the steak strips to lightly cover them, then dust with flour.
Heat the olive oil and butter in a large skillet. Quickly brown the steak strips on both sides in the skillet, then remove the steak from the pan.
Add the onion slices and mushrooms to the pan drippings and saute for several minutes until the onion is tender. Sprinkle with 1 teaspoon flour.
Put the steak back into the pan with the onions and mushrooms. Add the mushroom soup and beef broth. Lower the heat and stir in mustard. Cover the pan and cook over low heat for about 30 minutes.
Adjust seasoning to taste, adding salt and pepper as needed. Stir in the sour cream and white wine in the last few minutes, right before you serve.
Serve over cooked pasta. Garnish with chopped Italian parsley.