Season the beef cubes with salt and black pepper.
Heat the vegetable oil in a large skillet over medium-high heat. Add the beef cubes in batches and brown on all sides, about 3-4 minutes per batch. Transfer browned beef to the slow cooker.
Add the chopped onion and minced garlic to the skillet and sauté for 2-3 minutes until softened. Transfer to the slow cooker.
Pour beef broth and Worcestershire sauce into the slow cooker. Add dried thyme, dried rosemary, sliced carrots, and sliced celery. Stir to combine.
Cover and cook on low for 6 hours until the beef is tender.
About 30 minutes before serving, cook the wide egg noodles according to package instructions until al dente. Drain and set aside.
In a small bowl, whisk together the all-purpose flour and cold water until smooth to make a slurry.
Remove the slow cooker lid and stir in the flour slurry. Cover and cook on high for 15 minutes to thicken the sauce.
Stir the cooked egg noodles into the slow cooker until well combined and heated through.
Sprinkle chopped fresh parsley over the top before serving.