01 - Bring a large pot of salted water to a boil. Cook 12 oz wide egg noodles according to package instructions until al dente. Drain well, toss with 1 tbsp butter, and set aside keeping warm.
02 - Season 1 lb beef strips with 1/2 tsp salt and 1/2 tsp pepper. Dust evenly with 2 tbsp all-purpose flour to coat.
03 - Heat 1 tbsp butter and 1 tbsp olive oil in a large skillet over medium-high heat. Sear beef in batches for 1-2 minutes per side until browned but pink inside. Remove beef and tent with foil.
04 - Add remaining 1 tbsp butter to the skillet. Sauté onions for 3-4 minutes until softened. Add garlic and cook for 30 seconds until fragrant.
05 - Add mushrooms and cook for 6-8 minutes, stirring occasionally, until mushrooms release juices and start to brown.
06 - Pour in 1 cup beef broth, 1 tbsp Worcestershire sauce, and 1 tsp Dijon mustard. Scrape up browned bits from the bottom of the pan. Simmer for 3-4 minutes to slightly reduce.
07 - Lower heat to medium. Stir in 1 cup sour cream until smooth. Return beef and accumulated juices to the skillet. Simmer gently for 2-3 minutes until beef is heated through.
08 - Serve the beef and mushroom sauce over the prepared egg noodles. Sprinkle with chopped fresh parsley for garnish.