Melt 2 tablespoons butter in a large stockpot over medium-high heat.  Add the steak and season with a few generous pinches of salt and pepper.  Sauté for 5-7 minutes, stirring once every minute or so, until browned.  Remove steak from the pot with a slotted spoon and transfer to a separate plate.  Set aside.

Add the remaining 1 tablespoon butter to the stockpot, along with the mushrooms, onion and garlic.  Sauté for 5-6 minutes, or until the onion is soft and the mushrooms are browned.  Add in the white wine, and deglaze the pan by using a wooden spoon to scrape those tasty brown bits off the bottom of the pan. Let the mixture continue cooking for 3 minutes, until the liquid has reduced by about half.

Add in 5 1/2 cups beef stock, Worcestershire sauce, and egg noodles, and stir until combined.  Continue cooking until the mixture reaches a simmer.  Then reduce heat to medium-low and continue to simmer until the noodles are al dente, about 5-8 minutes, stirring occasionally.

Meanwhile, as the noodles are cooking, whisk the remaining 1/2 cup of beef stock and flour together in a small bowl until combined.  When the noodles are al dente, stir the flour mixture and sour cream into the soup until they are combined.  Continue simmering for 5 minutes.  Stir the cooked steak back into the soup. Taste, and season with salt and pepper as needed.

Serve hot, garnished with parsley if desired.