Brown the Beef: In a large stockpot, melt 2 tablespoons butter over medium-high heat. Add the steak, season with salt and pepper, and sauté for 5–7 minutes. Stir occasionally until the beef is browned. Remove with a slotted spoon and set aside.

Cook Vegetables: Add the remaining butter to the same pot. Stir in mushrooms, onion, and garlic. Sauté for 5–6 minutes until mushrooms are browned and onions softened.

Deglaze the Pot: Pour in the white wine and scrape the brown bits at the bottom with a wooden spoon. Let the mixture simmer for 3 minutes until reduced by half.

Add Broth and Noodles: Stir in 5 ½ cups beef stock, Worcestershire sauce, and egg noodles. Bring to a simmer, then reduce heat and cook until noodles are al dente, about 5–8 minutes. Stir occasionally.

Thicken the Soup: In a small bowl, whisk together the remaining ½ cup beef stock and flour. Stir this slurry into the soup along with the sour cream. Simmer gently for 5 minutes until thickened.

Finish and Serve: Return the cooked beef to the pot and stir until warmed through. Taste and adjust seasoning with salt and pepper. Garnish with fresh parsley and serve hot.