Slice steak into thin strips (like 1/4-inch thick). Make sure you are slicing against the grain of the meat. Sprinkle with salt and pepper and set aside.

Melt 2 tablespoons butter in a large skillet over medium heat and add mushrooms, onion, and garlic to pan. Saute for 5-8 minutes until mushrooms are browned and onions are very tender. Remove mushrooms, onions, and garlic from pan and set aside.

Slightly increase heat on pan and melt remaining tablespoons of butter. Add beef and saute, stirring, for 3-5 minutes or until pink is no longer visible.

While beef is cooking, whisk water, bouillon, flour, and Worcestershire sauce together until smooth. Add this mixture to the beef and return the mushroom mixture to the pan as well. Bring the sauce to a simmer and cook for 1-2 minutes to thicken. Remove pan from heat and stir in sour cream. Add additional salt and black pepper to taste. Serve over egg noodles or white rice.