Heat the olive oil in a large skillet over medium-high heat. Add sliced beef and sear for 1-2 minutes per side until just browned. Remove and set aside.
In the same skillet, melt butter. Sauté onions until translucent, then add garlic and mushrooms. Cook for about 5 minutes, stirring occasionally.
Sprinkle flour over the vegetables and stir well. Slowly pour in beef broth while whisking to avoid lumps.
Add Worcestershire sauce and simmer until the sauce begins to thicken, about 5 minutes.
Reduce heat to low. Stir in the sour cream until smooth and creamy. Do not boil once sour cream is added.
Return the beef to the skillet and simmer gently for 5 more minutes to heat through. Season with salt and pepper to taste.
Serve hot over cooked egg noodles or rice. Garnish with chopped parsley.
