In a large frying pan add vegetable oil, over medium heat sear mushrooms until golden and set aside. Add onions and sauté until they begin to soften. Add green peppers and cook until al dente. Set aside.
Over high heat, brown the meat (approx. ⅓ at a time). If necessary, drain fat.
Reduce heat to simmer and combine meat, mushrooms and onions and peppers.
Add 1 cup beef broth, mustard, salt and pepper. Cover and simmer for approximately 45 minutes, or until meat is tender.
Whisk 2 tbsp flour with ¼ cup of remaining beef broth until smooth with no lumps. Stir into meat mixture and cook until sauce thickens. Reduce heat to low. Prior to serving, add sour cream and stir.
Serve over hot egg noodles.