Prepare the ingredients: thinly slice the beef and mushrooms, and chop the onion and garlic.
Heat olive oil in a large pan over medium-high heat.
Sear the beef strips until browned, about 2-3 minutes, then remove from the pan.
In the same pan, add garlic, onion, and mushrooms. Sauté until softened, about 5 minutes.
Sprinkle flour over the mixture and stir to combine, cooking for an additional minute.
Gradually pour in beef broth and Worcestershire sauce, whisking constantly while bringing it to a simmer.
Return the beef to the pan and simmer for about 5 minutes until the beef is cooked through.
Reduce the heat to low and stir in the sour cream, mixing well until fully incorporated.
Season with salt and pepper to taste, adjusting as needed.
Serve hot, garnished with fresh parsley over cooked egg noodles or rice.