Wash tomatoes. Leave cores in and skin on. Cut in halves.
Start oven heating to 200 C (400 F).
Arrange tomato halves cut-sides down on ungreased, unsprayed baking sheets with high sides.
Bake for about 45 minutes, or until skins are wrinkling and turning brown, and tomatoes are soft.
Proceed in batches. If you need to remove cooked tomato halves from the baking sheets to free the sheets up for more, use a flipper to lift the halves off and place on platters to cool -- don't dump them in a bowl or you will make peeling them later triple the work.
Meanwhile, spray another baking sheet or dish with cooking spray, arrange the onion on it, lightly spray that onion, and bake until onions are golden brown -- about 20 minutes.
Let cooked tomato halves cool till it is safe to touch them.
Peel by pinching the skins in towards the centres of the tomatoes. The skins should come right off. (If you have a food mill, you can leave them on.)
Press the tomatoes through a food mill or sieve in batches to strain out the seeds (discard the seeds.)
Put tomato purée in pot.
Add the onion to the pot.
Add to the pot everything from the wine down to and including the bay leaves.
Bring to a boil, then lower to a simmer and simmer for about 20 minutes or desired thickness.
Remove and discard bay leaves.
Stir in either the citric acid OR the lemon juice.
Ladle sauce into heated jars, leaving 2 cm (½ inch) headspace.
Debubble, adjust headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process jars for 40 minutes; increase time as needed for your altitude.