frequently, until tender, about six minutes.
Add beef, in batches if necessary, and cook, breaking up with a wooden spoon, until browned.
Add chili powder, cinnamon, cumin, allspice, cloves, bay leaf, chocolate, beef broth, tomato sauce, cider vinegar, and cayenne pepper. Stir to mix well. Bring to a boil. Reduce heat to low; cover and simmer 11/2 hours, stirring occasionally.
Refrigerate overnight for best results. To serve, remove the bay leaf and reheat gently over medium heat. Serve over hot, drained spaghetti. Top with shredded Cheddar cheese.