Sandwich steak between two pieces of plastic wrap and pound with a mallet until it is an even ½ inch thick. Alternatively, if you have a thick piece of steak you can cut the steak in half widthwise to create two thin pieces of steak. Cut the steak into ½ inch wide strips about 3 inches long.
In a large bowl mix flour, salt, and pepper together. Toss steak strips in the flour mixture. Set floured steak aside.
Add half of the butter to a large skillet and heat over medium high heat until melted
Place half of the floured steak to the skillet and brown for 1-2 minutes per side. Set browned meat on a clean plate.
Add the remaining butter to the pan followed by the remaining beef and finish browning the meat. Add browned beef to the plate as well.
Add onions and cleaned sliced mushrooms to the skillet. Cover and cook slowly for 7-10 minutes stirring occasionally.
While the sauce simmers, cook the egg noodles according to the package instructions.
Stir in the Worcestershire and sour cream and cook with the mushrooms and onions for 2 minutes.
Add the beef to the pan and continue to cook for 5 minutes. Season with salt and pepper.
Serve over cooked egg noodles.