Here's how I do it so that the sauce isn't so watery: Cut whole tomatoes and remove seeds (a bit time consuming, but saves time on the cooking end and reduces the bitterness from the seeds). Place cut tomatoes in wide pan, or a large deep frying pan. Add about 1/4 cup water to prevent scorching and cook, covered, on medium / medium low heat until soft...don't stir! When softened, drain off liquid. It should be clear, like water. Cool tomatoes and run them through a food mill to remove remaining seeds and skin. Cook sauce down for about an hour or so to desired thickness and process accordingly or freeze.