01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package instructions until al dente. Drain well and toss with 1 tbsp butter; set aside and keep warm.
02 - While noodles cook, season beef strips with salt and pepper, then dust evenly with flour.
03 - In a large skillet over medium-high heat, heat 1 tbsp butter and olive oil. Sear beef in batches for 1-2 minutes per side until browned but still pink inside. Remove beef to a plate and tent with foil.
04 - In the same skillet, add remaining 1 tbsp butter. Sauté onions for 3-4 minutes until softened. Add garlic and cook for 30 seconds until fragrant.
05 - Add mushrooms and cook 6-8 minutes, stirring occasionally, until mushrooms release their juices and start to brown.
06 - Pour in beef broth, Worcestershire sauce, and Dijon mustard. Scrape up any browned bits from the bottom of the pan. Simmer for 3-4 minutes to slightly reduce.
07 - Lower heat to medium. Stir in sour cream until smooth do not boil. Return beef and any accumulated juices to the skillet. Simmer gently for 2-3 minutes until beef is just heated through. Adjust seasoning with salt and pepper as needed.
08 - Serve the beef and mushroom sauce over the egg noodles. Sprinkle with parsley for garnish.