Add the beef chunks, onion, carrots, celery, and garlic to the slow cooker.
Pour in the crushed tomatoes, tomato paste, and beef broth. Stir in the Italian seasoning, bay leaf, salt, and pepper until everything is combined.
Cover and cook on low for 8 hours, until the beef is very tender.
Remove the bay leaf. Shred the beef with two forks and stir it back into the sauce.
About 30 minutes before the ragu finishes, bring the water to a boil in a medium saucepan. Slowly whisk in the polenta and a pinch of salt.
Reduce the heat to low and cook, stirring often, until the polenta thickens and becomes creamy, about 20 to 25 minutes.
Stir the butter and Parmesan cheese into the polenta until smooth.
Spoon the creamy polenta into bowls, top with the beef ragu, and finish with extra Parmesan and fresh basil.