In a large skillet over medium heat, brown the ground beef with the chopped onion. Cook until beef is no longer pink and onions are soft.
Drain any excess grease from the skillet.
Whisk together beef broth, milk, cornstarch, garlic powder, paprika, salt, and pepper in a bowl. Pour into the skillet.
Stir in the egg noodles and bring to a simmer.
Cover and cook for 10–12 minutes, stirring occasionally, until noodles are tender and the sauce has thickened.
Remove from heat and stir in sour cream until well blended.
Garnish with parsley if using and serve hot.