Bring a large pot of salted water to a boil. Cook the egg noodles according to package directions until just tender, then drain and set aside.

Season the sliced beef with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Sprinkle the flour over the beef and toss lightly to coat.

Heat the olive oil in a large skillet over medium-high heat. Add the beef in a single layer and sear for 1 to 2 minutes per side until browned. Work in batches if needed. Transfer the beef to a plate.

Reduce the heat to medium. Add the butter, then stir in the mushrooms and onion. Cook for 6 to 8 minutes, stirring occasionally, until browned and softened.

Add the garlic, Worcestershire sauce, and Dijon mustard. Stir for about 30 seconds, just until fragrant.

Pour in the beef broth and scrape up any browned bits from the bottom of the skillet. Simmer for 5 to 7 minutes, until slightly reduced.

Lower the heat and return the beef and any juices to the pan. Simmer gently for 2 to 3 minutes, just until the beef is cooked through and tender.

Remove the skillet from the heat and stir in the sour cream and parsley. Taste and add the remaining salt and pepper as needed.

Serve the beef stroganoff over warm egg noodles and garnish with additional parsley.