Place the beef chunks, onion, garlic, carrots, and celery in the slow cooker.
Pour the crushed tomatoes and beef broth over the meat and vegetables.
Add the oregano, basil, salt, and pepper, then stir to combine.
Cover and cook on low for 8 hours until the beef is tender and pulls apart easily.
About 30 minutes before serving, bring the water to a boil in a saucepan.
Whisk in the cornmeal gradually and reduce heat to low. Stir often for 20 minutes until thick.
Stir the Parmesan, butter, and heavy cream into the polenta until smooth.
Shred the beef in the slow cooker with two forks and mix it into the sauce.
Spoon the polenta into bowls, top with the beef ragu, and sprinkle with fresh parsley.