01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package directions. Drain, toss with 1 tbsp butter, and set aside.
02 - In a bowl, toss beef strips with flour, salt, and black pepper until evenly coated.
03 - Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Add beef in a single layer and sear for 1 to 2 minutes per side until browned but not fully cooked. Remove beef to a plate and cover loosely.
04 - Reduce heat to medium. Add remaining 1 tbsp butter to the skillet. Sauté onions for 2 to 3 minutes until softened. Add garlic and cook for 30 seconds.
05 - Add mushrooms and cook, stirring occasionally, until browned and their liquid has evaporated, about 5 to 7 minutes.
06 - Stir in beef broth, Worcestershire sauce, and Dijon mustard. Scrape up any browned bits from the skillet. Simmer for 5 minutes to reduce slightly.
07 - Return beef and any accumulated juices to the skillet. Simmer gently for 2 to 3 minutes until beef is just cooked through.
08 - Reduce heat to low. Stir in sour cream and chopped parsley until smooth and warmed through, avoiding boiling. Adjust seasoning with salt and pepper as needed.
09 - Serve beef and mushroom gravy over buttered egg noodles. Garnish with extra parsley if desired.