Slice the beef into thin strips, season with salt and pepper, and pat dry. Heat skillet over medium-high heat, add butter and olive oil, then cook beef for 3-4 minutes until browned. Remove and set aside.

In the same skillet, reduce heat to medium, add onions and garlic. Sauté for 2-3 minutes until translucent. Add sliced mushrooms, cooking for 5-6 minutes until brown.

Sprinkle flour over the vegetables, stir, then slowly add beef broth while stirring to avoid lumps. Simmer for 5-7 minutes until thickened.

Stir in sour cream until smooth, then return beef to skillet and simmer for 2-3 minutes to meld flavors.

Cook egg noodles according to package instructions until al dente, then drain.

Serve beef stroganoff over noodles, garnished with chopped parsley.