01 - Cook the egg noodles in a large pot of boiling salted water according to package instructions. Drain, toss with a little butter if desired, and set aside.
02 - In a bowl, toss the beef strips with flour, salt, and pepper until evenly coated.
03 - Heat 1 tablespoon of butter and the oil in a large skillet over medium-high heat. Add the beef in batches, searing quickly until browned on all sides (about 2 minutes per batch). Remove the beef and set aside.
04 - In the same skillet, add remaining butter. Sauté the onion for 2–3 minutes, then add the mushrooms and cook until softened and golden, about 5 minutes. Stir in the garlic and cook for 1 minute more.
05 - Add tomato paste and stir until well combined. Pour in beef broth, scraping up any browned bits. Bring to a gentle simmer and let reduce for 5 minutes.
06 - Lower the heat to medium-low. Stir in sour cream, Dijon mustard, and Worcestershire sauce. Mix until smooth and gently heated—do not boil.
07 - Return the seared beef and any juices to the skillet. Stir until just heated through and coated in the sauce. Taste and adjust seasoning with salt and pepper. Serve the beef stroganoff hot over the prepared egg noodles. Garnish with chopped parsley if desired.