01 - Generously season beef chunks with salt and pepper on all sides.
02 - Heat a large skillet over medium-high heat. Sear beef on all sides until browned, approximately 2–3 minutes per side. Transfer browned beef to the slow cooker.
03 - Add onion, carrots, celery, and garlic to the same skillet. Sauté for 3–4 minutes until softened and fragrant, then transfer vegetables to the slow cooker.
04 - Pour red wine into the skillet and deglaze by scraping up the browned bits from the bottom. Simmer for 2 minutes, then add the wine mixture to the slow cooker.
05 - Add crushed tomatoes, tomato paste, beef broth, oregano, thyme, bay leaves, and red pepper flakes to the slow cooker. Stir everything together until well combined.
06 - Cover and cook on low setting for 8 hours, or on high for 4–5 hours, until the beef is very tender and easily shreds apart.
07 - Remove and discard the bay leaves. Shred the beef using two forks, then stir it back into the sauce. Taste and adjust seasoning with additional salt and pepper if needed.
08 - Serve hot over cooked pasta or creamy polenta. Garnish with fresh chopped parsley and grated Parmesan cheese if desired.