01 - Heat olive oil in a large skillet over medium-high heat. Brown beef pieces in batches for 2–3 minutes per side. Transfer browned beef to slow cooker.
02 - Add onion, garlic, carrots, and celery to the skillet. Cook for 5 minutes until softened. Stir in tomato paste and cook for 1 minute.
03 - Pour red wine into the skillet, scraping up browned bits. Transfer vegetable mixture and juices to slow cooker over the beef.
04 - Add crushed tomatoes, beef broth, oregano, basil, bay leaf, salt, black pepper, and red pepper flakes to slow cooker. Stir to combine.
05 - Cover and cook on low for 8 hours or high for 4 hours, until beef is fork-tender.
06 - Remove bay leaf. Shred beef with two forks and mix back into sauce. Adjust seasoning as needed.
07 - Bring water and salt to a boil in a large 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. Top with beef ragu. Garnish with chopped parsley and additional Parmesan if desired.