Bring a large pot of salted water to a boil. Cook the egg noodles according to package directions until just tender, then drain and toss with 1 tablespoon of the butter. Set aside and cover to keep warm.

Heat 1 tablespoon of butter in a large skillet over medium-high heat. Add the sliced beef in a single layer and cook until browned on both sides, about 3 to 4 minutes. Remove the beef to a plate and set aside.

Lower the heat to medium and add the remaining tablespoon of butter to the same skillet. Stir in the onion and mushrooms and cook until the onion softens and the mushrooms release their liquid, about 5 minutes.

Add the garlic and cook for 30 seconds until fragrant. Sprinkle the flour over the vegetables and stir for 1 minute to cook out the raw taste.

Slowly pour in the beef broth while stirring to avoid lumps. Bring the mixture to a simmer and cook until it thickens slightly, about 3 minutes.

Return the beef and any juices to the skillet. Remove the pan from the heat and stir in the sour cream until fully combined. Season with salt and black pepper.

Divide the buttered egg noodles among four plates. Spoon the beef stroganoff over the noodles and sprinkle with chopped parsley before serving.