01 - Season beef chunks with salt and black pepper.
02 - In a large skillet over medium-high heat, sear beef on all sides until browned, about 5 minutes total.
03 - Place onions, garlic, carrots, and celery in the bottom of the slow cooker.
04 - Arrange seared beef on top of the vegetables in the slow cooker.
05 - Add crushed tomatoes, red wine, tomato paste, and beef broth to the slow cooker. Sprinkle oregano, thyme, bay leaves, remaining salt, black pepper, and red pepper flakes if desired.
06 - Cover and cook on low heat for 8 hours or on high for 5 hours, until beef is very tender and easy to shred.
07 - Discard bay leaves. Using two forks, shred the beef directly in the slow cooker and stir thoroughly to combine with the sauce.
08 - Taste and adjust seasoning as needed.
09 - Ladle hot ragu over cooked pasta or creamy polenta. Garnish with chopped fresh herbs and, if desired, grated Parmesan cheese.