01 - Heat olive oil in a large skillet over medium-high heat. Sear the beef pieces in batches until browned on all sides, about 2 to 3 minutes per batch. Transfer browned beef to the slow cooker.
02 - Add onion, garlic, carrots, and celery to the same skillet. Cook for 5 minutes until softened. Stir in tomato paste and cook for 1 minute to develop flavor.
03 - Deglaze the skillet with red wine, scraping up browned bits. Pour the vegetable mixture and juices over the beef in the slow cooker.
04 - In the slow cooker, add crushed tomatoes, beef broth, oregano, basil, bay leaf, kosher salt, black pepper, and optional red pepper flakes. Stir to combine thoroughly.
05 - Cover and cook on LOW for 8 hours or HIGH for 4 hours until beef is fork-tender.
06 - Remove bay leaf from the slow cooker. Shred beef with two forks and stir back into the sauce. Adjust seasoning as needed.
07 - Bring water and kosher salt to a boil in a large saucepan. Gradually whisk in polenta to prevent lumps. Reduce heat to low and cook, stirring frequently, for 20 to 25 minutes until thick and creamy.
08 - Stir in whole milk, unsalted butter, and grated Parmesan cheese until smooth and creamy.
09 - Spoon creamy polenta into bowls and top with a generous portion of beef ragu. Garnish with chopped parsley and additional Parmesan as desired.