Bring a pot of salted water to a boil and cook the egg noodles until tender. Drain them, return to the pot, and toss with 1 tablespoon of butter. Cover to keep warm.
Melt the remaining 2 tablespoons of butter in a large skillet over medium heat. Add the onion and mushrooms and cook until the onion softens and the mushrooms release their liquid.
Stir in the garlic and cook for 30 seconds. Sprinkle the flour over the vegetables and stir for one minute to cook out the raw taste.
Slowly pour in the beef broth while stirring. Add the Worcestershire sauce, salt, and pepper. Simmer until the sauce thickens slightly.
Add the cubed meatloaf to the skillet and stir gently until heated through, about 3 minutes.
Remove the skillet from the heat and stir in the sour cream until the sauce is smooth. Spoon the meatloaf mixture over the buttered noodles and sprinkle with parsley before serving.