01 - Heat olive oil in a large skillet over medium-high heat. Brown beef pieces in batches, about 2–3 minutes per batch, then transfer to the slow cooker.
02 - Add onion, garlic, carrots, and celery to the skillet and sauté for 5 minutes until softened. Stir in tomato paste and cook for 1 minute.
03 - Deglaze skillet with red wine, scraping up browned bits. Pour vegetable mixture and juices over beef in slow cooker.
04 - Add crushed tomatoes, beef broth, oregano, basil, bay leaf, salt, black pepper, and red pepper flakes. Stir to blend.
05 - Cover and cook on LOW for 8 hours or HIGH for 4 hours, until beef is tender.
06 - Remove bay leaf. Shred beef with forks and return to sauce. Adjust seasoning as needed.
07 - Bring water and salt to a boil in a saucepan. Gradually whisk in polenta. Reduce heat to low and cook, stirring frequently, for 20–25 minutes until thick and creamy.
08 - Stir in milk, butter, and Parmesan cheese until smooth.
09 - Spoon creamy polenta into bowls and top with beef ragu. Garnish with parsley and extra Parmesan if desired.