01 - Season the beef strips thoroughly with salt and pepper.
02 - Heat 1 tbsp olive oil and 1 tbsp butter in a large skillet over medium-high heat. Add beef in batches and sear quickly for 1–2 minutes per side. Remove beef to a plate and set aside.
03 - In the same skillet, add remaining olive oil and butter. Sauté onions until soft, about 3 minutes. Add garlic and cook 1 minute more.
04 - Add mushrooms, sauté until browned and their liquid has evaporated, about 5 minutes.
05 - Sprinkle in flour and stir well to coat vegetables. Cook for 1 minute.
06 - Gradually add beef broth, stirring constantly to prevent lumps. Add Worcestershire sauce and Dijon mustard. Bring to a gentle simmer and cook for 5 minutes, stirring occasionally, until slightly thickened.
07 - While sauce simmers, cook egg noodles according to package directions. Drain and set aside.
08 - Lower heat, return beef (with any juices) to the skillet. Warm gently for 2–3 minutes.
09 - Remove skillet from heat. Stir in sour cream and half the parsley until sauce is smooth.
10 - Serve stroganoff over egg noodles, garnished with remaining parsley.