In a large skillet, heat the olive oil over medium heat. Add the chopped onions and garlic, sautéing until soft and fragrant (about 3-4 minutes).
Add the ground beef to the skillet, breaking it apart with a wooden spoon. Cook until browned (about 5-6 minutes), then drain any excess fat.
Stir in the sliced mushrooms and cook until they begin to soften (about 3 minutes).
Sprinkle the all-purpose flour over the beef mixture, stirring to coat evenly, and cook for another minute.
Gradually add the beef broth, Worcestershire sauce, and Dijon mustard, stirring constantly until the mixture thickens.
Lower the heat and stir in the sour cream, mixing well. Season with salt and pepper to taste. Allow the sauce to simmer on low heat while you prepare the noodles.
In a pot of boiling salted water, cook the egg noodles according to package instructions until al dente. Drain and set aside.
Serve the ground beef stroganoff over the cooked egg noodles, garnishing with parsley if desired.