01 - Generously season beef chunks with salt and pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Sear beef on all sides until browned, about 2–3 minutes per side. Transfer beef to slow cooker.
03 - In the same skillet, cook onion, carrots, and celery for 4–5 minutes until softened. Stir in garlic and tomato paste; cook for 1 minute. Transfer mixture to slow cooker.
04 - Add crushed tomatoes, beef broth, red wine, oregano, thyme, basil, red pepper flakes if using, and bay leaves to slow cooker. Stir gently to combine.
05 - Cover and cook on low for 8 hours until beef is tender and shreds easily with a fork.
06 - Remove beef, shred with two forks, and return to sauce. Discard bay leaves. Adjust seasoning with salt and pepper to taste.
07 - Prepare pappardelle according to package instructions until al dente. Drain thoroughly.
08 - Toss pasta with ragu sauce or serve sauce atop pasta. Garnish with Parmesan and parsley.