01 - Bring a large pot of salted water to a boil. Cook egg noodles according to package directions. Drain, toss with 1 tablespoon unsalted butter, and set aside.
02 - In a bowl, combine beef strips with all-purpose flour, salt, and black pepper until evenly coated.
03 - Heat 1 tablespoon unsalted butter and olive oil in a large skillet over medium-high heat. Add beef strips 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 tablespoon butter to the skillet. Cook chopped onions for 2 to 3 minutes until softened, then add minced garlic and cook for 30 seconds.
05 - Add sliced mushrooms and cook, stirring occasionally, until browned and moisture has evaporated, about 5 to 7 minutes.
06 - Stir in beef broth, Worcestershire sauce, and Dijon mustard. Scrape any browned bits from the pan. Simmer for 5 minutes to reduce slightly.
07 - Return beef along with any accumulated juices to the skillet. Simmer gently for 2 to 3 minutes until beef is cooked through.
08 - Reduce heat to low. Stir in sour cream and chopped parsley until fully incorporated and heated through without boiling. Adjust seasoning with salt and pepper to taste.
09 - Plate buttered egg noodles and top with beef stroganoff. Garnish with additional chopped parsley.