01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package instructions. Drain and set aside, tossing with a little butter if desired.
02 - While noodles cook, season beef strips with salt and pepper.
03 - Heat 1 tbsp butter in a large skillet over medium-high heat. Add half the beef and sear until just browned, about 1–2 minutes per side. Remove beef to a plate. Repeat with remaining beef.
04 - Reduce heat to medium. Add remaining 1 tbsp butter to the skillet. Sauté onion for 3 minutes until translucent. Add garlic and mushrooms; cook 5–6 minutes, stirring frequently, until mushrooms are golden and liquid evaporates.
05 - Stir in flour and cook for 1 minute to remove raw taste.
06 - Gradually pour in beef broth while stirring. Add Worcestershire sauce, tomato paste, and Dijon mustard. Scrape browned bits from the pan to deepen flavor.
07 - Allow sauce to simmer for 3–4 minutes until slightly thickened.
08 - Lower heat and stir in sour cream until smooth without boiling. Return beef and any accumulated juices to skillet. Cook 2–3 minutes until beef is heated through.
09 - Plate beef mixture over egg noodles and garnish with chopped parsley.