Bring 3 quarts of water to a boil in a large stock pot. Add the noodles and cook until tender, about 10 minutes. Drain then add back to the pot with the butter and stir for the butter to melt. Season with ½ teaspoon kosher salt and ¼ teaspoon black pepper and cover with a lid.

Meanwhile, add the ground beef to a large skillet over medium-high heat. Cook for 8 minutes or until cooked through, breaking up the beef with a flat bottom spatula. Add the mushrooms, onion, garlic, ½ teaspoon kosher salt, and ½ teaspoon of black pepper. Cook until the mushrooms and onions soften, stirring often, about 3-4 minutes.

Add the Worcestershire sauce and tomato paste and stir well to combine. Sprinkle with the flour and cook for 1-2 minutes, stirring. Add the beef stock, stir, and cook for 3-4 minutes for the flavors to come together and the sauce to thicken. Fold the sour cream into the beef mixture until smooth and heated through.

To serve, top the egg noodles with the hamburger stroganoff, add a fresh dollop of sour cream, and sprinkle with chopped green onion or minced chives.