Place the beef stew meat, sliced onion, and mushrooms in the slow cooker.
In a bowl, whisk the beef broth, Worcestershire sauce, paprika, salt, pepper, and flour until smooth. Pour the mixture over the beef and vegetables.
Cover and cook on low for 8 hours until the beef is fork-tender.
Stir the sour cream into the slow cooker until the sauce is fully combined and creamy.
While the sauce finishes, cook the egg noodles in a large pot of boiling water according to package directions. Drain well.
Spoon the beef and sauce over the hot noodles and sprinkle with chopped parsley before serving.