01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package directions. Drain and set aside, optionally tossing with a bit of butter.
02 - While noodles cook, season beef strips evenly with salt and black pepper.
03 - Heat 1 tablespoon butter in a large skillet over medium-high heat. Add half the beef and sear until lightly browned, about 1–2 minutes per side. Remove to a plate and repeat with remaining beef.
04 - Reduce heat to medium. Add remaining 1 tablespoon butter to the skillet. Sauté onion for 3 minutes until translucent, then add garlic and mushrooms. Cook 5–6 minutes, stirring occasionally, until mushrooms turn golden and any released liquid evaporates.
05 - Sprinkle flour over the vegetable mixture and cook, stirring constantly, for 1 minute.
06 - Gradually pour in beef broth while stirring. Incorporate Worcestershire sauce, tomato paste, and Dijon mustard. Scrape any browned bits from the pan to enhance flavor.
07 - Allow sauce to simmer gently for 3–4 minutes until it thickens slightly.
08 - Lower heat and stir in sour cream until fully integrated, ensuring it does not boil. Return beef and accumulated juices to the skillet and cook for 2–3 minutes until heated through.
09 - Plate the beef and mushroom sauce over the cooked egg noodles. Garnish with chopped fresh parsley before serving.