Heat olive oil in a large skillet over medium-high heat.
Add beef cubes in batches and brown on all sides, about 5 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add chopped onion, carrots, and celery. Cook until softened, about 5 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Pour in red wine to deglaze the skillet, scraping up any browned bits from the bottom. Let it simmer for 2 minutes.
Transfer the vegetable and wine mixture to the slow cooker with the beef.
Add crushed tomatoes, beef broth, tomato paste, dried oregano, dried thyme, crushed red pepper flakes, and bay leaf to the slow cooker. Stir to combine.
Season with salt and freshly ground black pepper to taste.
Cover and cook on low for 6 hours, or until the beef is very tender and easily shredded.
About 15 minutes before serving, bring a large pot of salted water to a boil.
Cook the pappardelle pasta according to package instructions until al dente. Drain and set aside.
Remove the bay leaf from the ragu. Using two forks, shred the beef into the sauce and stir well.
Serve the beef ragu over the cooked pappardelle pasta.
Sprinkle grated Parmesan cheese and chopped fresh parsley on top before serving.