Start by cutting the tomatoes in half and cutting the stem part out. Place cut side down on a rimmed baking sheet, WITHOUT any cooking oil or spray.
Roast 45 to 50 minutes at 450°F. Take them out and let them cool a bit before you start taking the skins off.
Leave the tomatoes lying flat and start to pinch the skins off (simply by pinching them towards the center). If the skin isn’t coming off effortlessly, that means they needed to be roasted longer.
Collect all the tomato halves, and discard the liquid (or refrigerate for use in something else). Now at this point you can either run it thru a food mill / sieve for a smooth sauce, or you can blend it in a food processor for a bit chunkier of a sauce, or you could even leave as is and have more like diced tomatoes or a very rustic sauce. Just depends on your preference.
While your sauce is still hot put in either quart or pint jars, leaving 1/2 inch headspace. Add 2 tablespoons bottled lemon juice or 1/2 teaspoon citric acid to each quart – add 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid to each pint. This insures that the sauce is acidic enough to be safely water bath canned since tomatoes vary quite a bit in acidity.
Wipe the rims with a wet cloth and adjust your two piece lids. Process pints 40 minutes and quarts 45 minutes in a boiling water bath canner.
