From http://whatscookingamerica.net/Beef/CincinnatiChili.htm
In a large frying pan over medium-high heat, sauté onion, ground beef, garlic, and chili powder until ground beef is slightly cooked.
Add allspice, cinnamon, cumin, cayenne pepper, salt, unsweetened cocoa or chocolate, tomato sauce, Worcestershire sauce, cider vinegar, and water. Reduce heat to low and simmer, uncovered, 1 hour 30 minutes. Remove from heat.
Cook spaghetti according to package directions and transfer onto individual serving plates (small oval plates are traditional).
Ladle Cincinnati Chili mixture over the cooked spaghetti and serve with toppings of your choice.
Oyster crackers are served in a separate container on the side.