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 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 for 1–2 minutes per side until just browned. Transfer to a plate. Repeat with remaining beef.
04 - Reduce heat to medium. Add remaining 1 tablespoon butter to the skillet. Sauté onion for 3 minutes until translucent. Add garlic and mushrooms, cooking for 5–6 minutes until mushrooms turn golden and moisture evaporates.
05 - Sprinkle flour over the vegetables and cook, stirring, for 1 minute to remove raw taste.
06 - Gradually whisk in beef broth, then stir in Worcestershire sauce, tomato paste, and Dijon mustard. Scrape browned bits from the pan for flavor integration.
07 - Allow sauce to simmer gently for 3–4 minutes until it thickens slightly.
08 - Lower heat and stir in sour cream until smooth, avoiding boiling. Return seared beef and any accumulated juices to the skillet. Cook an additional 2–3 minutes until beef is heated through.
09 - Plate the beef mixture over the cooked egg noodles and garnish with chopped fresh parsley.