In a 6 or 8 quart slow cooker, add the beef broth, tomato sauce, vinegar and Worcestershire sauces, all the dry seasonings, bay leaf and grated chocolate. Whisk to combine.
Break up the ground sirloin into smaller pieces and add to the slow cooker.
Cover and cook on high for 4 hours or low for 8 hours.
Remove the bay leaf and use a potato masher to break up any larger pieces of the cooked beef.
Serve the slow cooker Cincinnati chili atop spaghetti and topped with plenty of freshly grated sharp cheddar cheese.