Brown The Beef, Onions And Mushrooms In Butter For 10 Minutes. Stir In Flour, Mustard And Broth. Cover And Simmer For 1 Hour. Stir In Sour Cream, Salt And Pepper. Simmer For 2 Minutes. Add Parsley And Simmer For 5 More Minutes. Do Not Boil Or The Sour Cream With Curdle. Serve.