Preheat the oven to 400˚F.
Warm the olive oil over medium heat in a heavy bottomed, oven-safe pot. The pot should be able to hold 8 cups, or 1 quart, of sauce comfortably. Add the onions and sauté for 5 - 7 minutes, or until softened.
Stir in all of the remaining ingredients and bring to a gentle simmer, about 7 - 8 minutes. Slide the pot, uncovered, into the oven. Place a baking sheet on a rack below the pot, in case it boils over - although I've never yet had this happen.
Roast for 1 hour, and remove from the oven. Correct for any seasoning, and cool before ladling into jars.
The sauce can keep in the refrigerator for up to 2 weeks, and in the freezer for up to 6 months.