I bought 20 lbs of grade B tomatoes at the market for $5. (They’re local tomatoes that are a bit soft, or a bit strangely shaped, or that have blemishes on their skin – perfect for canning.) I cored and quartered them and cooked them for a couple hours to soften them, then ran them through my food mill to remove the skins and seeds. I put them back int the pot on the back burner, uncovered, and cooked them at 2 (just warmer than low) for about 12 hours, then reduced the heat to low and continued cooking them for another 18 hours. I stirred them when I thought to, which wasn’t very often. By the end of their 30 hour cooking, they’d reduced by half and thickened nicely. I put them in 8 ounce, 12 ounce, and 1 L jars for various purposes and froze them. They’ll be great in soups and, of course, tomato sauce.