In a large nonstick skillet, brown the ground beef over medium-high heat, breaking up any large chunks with a wooden spoon. Drain beef on a paper towel-lined plate and set aside. Return the skillet to the burner over medium heat.
Melt the 4 tablespoons butter in the pan. Add the mushrooms and onion and cook for 6 to 7 minutes or until onions are softened and mushrooms lightly browned, stirring occasionally. Return the browned beef to the skillet along with the garlic, Worcestershire, salt and pepper, and cook just until you start to smell garlic, about 1 minute. Add the flour and cook for 1 minute. Stir in the stock and bring to a boil, reduce heat, and simmer until mixture is thickened, about 8 minutes. Off heat, fold in the sour cream and chives, reserving some chives for garnish. Keep warm while cooking the noodles.
Cook the noodles according to package directions and drain. Return the noodles to the pot, add the butter, garlic salt and chives, and toss to coat. Serve stroganoff over the noodles.