Slice beef into thin strips
Season beef with salt and pepper
Heat oil or butter in a skillet over medium-high heat
Sear beef quickly until browned
Remove beef from skillet and set aside
Add chopped onion to the skillet
Cook onion until softened
Add sliced mushrooms
Cook until mushrooms release liquid and brown
Add minced garlic
Cook for 30 seconds
Stir in flour
Cook for 1 minute
Pour in beef broth
Add Worcestershire sauce
Stir until sauce thickens
Reduce heat to low
Stir in sour cream
Return beef to the skillet
Warm gently without boiling
Serve over egg noodles, rice, or mashed potatoes
Garnish with parsley if desired