Season the beef cubes with salt and black pepper evenly.
Heat 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.
In the same skillet, add diced onion and cook for 3 minutes until softened. Add minced garlic and cook for 30 seconds until fragrant. Transfer onion and garlic to the slow cooker.
Add beef broth, water, tomato paste, Worcestershire sauce, dried thyme, and dried rosemary to the slow cooker. Stir to combine.
Add sliced carrots and celery to the slow cooker. Cover and cook on low for 6 hours until beef is tender.
About 30 minutes before serving, cook the egg noodles according to package instructions until al dente. Drain and set aside.
In a small bowl, whisk together cornstarch and cold water until smooth.
Remove the slow cooker lid and stir in the cornstarch mixture. Cover and cook on high for 15 minutes until the sauce thickens.
Add the cooked egg noodles to the slow cooker and gently stir to combine and heat through.
Sprinkle chopped fresh parsley over the dish before serving.