1. Put all ingredients in a large saucepan and stir.
2. Heat on medium-high until mixture comes to a boil.
3. Turn heat down immediately, loosely cover pan with lid, and simmer very slowly for 20 to 30 minutes, being sure to stir occasionally.
4. Cook spaghetti according to package directions.
5. Remove bay leaf from sauce and spoon sauce over hot spaghetti. Top with grated Parmesan cheese if desired.