Cook egg noodles according to package directions, drain, and set aside.
Heat olive oil in a large skillet over medium-high heat. Season beef with salt and pepper, then cook for 3-4 minutes until browned. Remove and set aside.
In the same skillet, add onions and mushrooms. Cook for 5-6 minutes until softened and golden. Add garlic and cook for 1 minute more.
Sprinkle flour over the vegetables and stir well. Gradually add beef broth, stirring constantly until the sauce thickens, about 3 minutes.
Reduce heat to low and stir in sour cream and Dijon mustard until smooth.
Return beef to the skillet and simmer for 2-3 minutes. Serve over cooked noodles and garnish with fresh parsley.