01 - Bring a large pot of salted water to a boil for the egg noodles.
02 - In a bowl, toss the beef strips with flour, salt, and pepper.
03 - Heat 1 tablespoon of butter and the vegetable oil in a large skillet over medium-high heat. Quickly sear the beef in batches for 1 to 2 minutes until browned but not fully cooked. Remove and set aside.
04 - In the same skillet, add the remaining butter. Sauté the onion for 2 minutes until translucent. Add mushrooms and cook until golden and most moisture has evaporated, about 5 minutes. Stir in garlic and cook for 30 seconds.
05 - Deglaze the pan with white wine or beef broth, scraping up browned bits. Stir in tomato paste and Dijon mustard. Pour in beef broth, bring to a simmer, and cook for 5 minutes.
06 - Reduce heat to low. Stir in sour cream until smooth, avoiding boiling. Return beef and any juices to the pan and cook gently for 2 to 3 minutes until beef is just cooked through.
07 - Meanwhile, cook egg noodles according to package instructions. Drain and optionally toss with butter.
08 - Place the stroganoff over the egg noodles and sprinkle with fresh parsley before serving.