• 15 lb. ripe Italian plum tomatoes, halved
• 4 yellow onions, halved through the root end
• 4 branches fresh rosemary, thyme, oregano, basil or other herb of choice
• Salt and freshly ground pepper, to taste
• 1/4 cup fresh lemon juice
• Good-quality extra-virgin olive oil
• 6 to 8 fresh basil sprigs

1. Put the tomatoes, along with their juice, in a large heavy-bottomed pot. Add the onions and herb branches, and season with salt and pepper. Set over medium-high heat and bring to a boil. Reduce the heat to low and simmer very gently, stirring often with a wooden spoon, until the tomato flesh is completely soft, 2 to 3 hours.
2. Let the tomatoes cool for about 1 hour. Discard the onions and herb branches. Pass the tomatoes through a food mill into another large clean pot, discarding the solids. Add the lemon juice and a drizzle of olive oil, set over medium heat and heat, stirring, until hot.
3. Meanwhile, wash 6 to 8 pint canning jars with their lids and rings in hot soapy water and rinse them, then place in a large pan or bowl and cover with boiling water. Keep them in the hot water until ready to use. Remove the jars from the water and pour out any water. Arrange the jars together for easy filling. Put a basil sprig in each jar. At the same time, fill a large pot (large enough to hold the jars in a single layer) with warm water to a depth of 4 inches. A canning kettle with a rack is ideal.
4. To process the tomato sauce, use a sterilized glass measuring cup and a funnel to pour about 1 cup of the hot sauce into each jar, leaving about 1/2 inch of headspace. Using a paper towel dipped in hot water, wipe the rims clean. Place the lid on each jar, then screw on the rings. Arrange the jars in the water in the pot (the water should cover the jars by 2 inches) and bring to a boil over medium-high heat. Boil for 35 minutes.
5. Using tongs, remove the jars from the water and place on a tray lined with a kitchen towel. Let the jars cool undisturbed for 12 hours. If the jars have sealed properly, the lids will be slightly indented and not springy to the touch. If a jar did not seal properly, either repeat the water bath process or refrigerate and use the sauce. Makes 6 to 8 pints.

Found: http://www.williams-sonoma.com/recipe/simplest-tomato-sauce.html