01 - Pat beef dry and season evenly with salt and pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Brown beef on all sides, about 4 to 5 minutes per batch, then transfer to slow cooker.
03 - In the same skillet, add onion, carrots, celery, and garlic. Cook, stirring occasionally, until softened, about 4 to 5 minutes. Transfer to slow cooker.
04 - Add crushed tomatoes, tomato paste, beef broth, red wine, oregano, thyme, bay leaves, and red pepper flakes to the slow cooker. Stir to incorporate.
05 - Cover and cook on low for 8 hours or on high for 4 to 5 hours, until beef is tender and easily shredded.
06 - Remove bay leaves and shred the beef with two forks. Stir the mixture and adjust seasoning with salt and pepper.
07 - Thirty minutes before serving, bring water or broth to a boil in a large saucepan. Gradually whisk in polenta, reduce heat to low, and cook, stirring frequently, for 20 to 25 minutes until thick and creamy.
08 - Stir in butter, grated Parmesan, and season with salt to taste.
09 - Ladle polenta into bowls, top with beef ragu, and garnish with chopped parsley and additional Parmesan cheese.