Heat an 8- to 10 quart heavy bottom pop and add the oil, onion and garlic. Sauté until the onion is clear. Add the remaining ingredients except the butter and salt and pepper. Bring to a simmer and gently cook, uncovered, for 4 hours, stirring often. Finish by stirring in the butter and salt and pepper to taste.
It's pretty easy to half the recipe, just half the onion, fresh tomatoes, canned tomatoes, butter and ease back on everything else (just a little bit).
I find the above recipe makes around 12 to 14 cups of sauce, store and freeze in one cup small freezer bags.