In a skillet over medium heat, brown the beef stew meat on all sides (about 5-7 minutes).
Transfer the browned beef to the slow cooker. Add the chopped onion, minced garlic, and sliced mushrooms.
In a bowl, whisk together the beef broth, Worcestershire sauce, dried thyme, salt, and black pepper. Pour this mixture over the beef and vegetables in the slow cooker.
Cover and cook on low for 6 hours or until the beef is tender.
About 30 minutes before serving, in a small bowl, combine the sour cream and all-purpose flour. Stir until smooth, then add it to the slow cooker and mix well.
Continue cooking for an additional 30 minutes on low to heat through.
While the stroganoff is finishing, cook the egg noodles according to package instructions. Drain and set aside.
Serve the beef stroganoff over the egg noodles and garnish with chopped parsley.