01 - Season the sliced beef with salt and pepper, then toss with flour to coat lightly.
02 - Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Add beef in batches, searing quickly until browned (about 1–2 minutes per side). Remove beef and set aside.
03 - In the same skillet, add remaining butter. Sauté onions for 2–3 minutes until soft. Add mushrooms and cook until browned and their liquid is mostly evaporated, about 5 minutes. Stir in garlic and cook for 1 minute.
04 - Return beef (and juices) to the pan. Add Dijon mustard and Worcestershire sauce, stirring to combine.
05 - Pour in beef broth, scraping up any browned bits. Bring to a simmer, reduce heat to low, and cook for 5 minutes until slightly thickened.
06 - Meanwhile, cook egg noodles according to package instructions. Drain and toss with a little butter, if desired.
07 - Remove skillet from heat. Stir in sour cream until smooth and warmed through—do not boil. Adjust seasoning with salt and pepper.
08 - Serve the beef stroganoff over egg noodles. Garnish with fresh parsley.