Prepare the Beef: Season the beef strips with salt and pepper.
Cook the Beef: Heat 1 tbsp oil in a large skillet over medium-high heat. Sear the beef in batches until browned. Remove and set aside.
Sauté the Vegetables: In the same skillet, add the remaining oil. Sauté the onions until softened, then add the garlic and mushrooms. Cook until the mushrooms are golden.
Make the Sauce: Stir in the beef broth, Dijon mustard, and paprika. Return the beef to the skillet and simmer for 5-7 minutes.
Finish with Sour Cream: Remove from heat and stir in the sour cream until the sauce is creamy. Adjust seasoning if needed.
Serve: Serve over cooked egg noodles, garnished with fresh parsley.