Adapted from Marcella Hazan.
Puree a 28 oz can of tomatoes in your blender. Pour into a saucepan, adding a teaspoon of salt,a quarter teaspoon of sugar, a stick of butter, and a peeled onion, halved. Bring to a simmer and simmer for 30-40 minutes, stirring occasionally.. If it reduces too quickly, add a little water periodically.
Remove the onion. (I end up scraping the sauce off of the onion before tossing it.) Use whenever you are tempted by bottled sauces.