Not that long ago, really. Last fall. At the end of the season, I got a great deal on tomatoes, and I planned on canning them. I started out with canned whole tomatoes and then I progressed to tomato sauce and salsa and chili sauce. I started running out of storage space and jars.
I decided that it made sense to reduce the remaining tomatoes as much as possible, and that meant tomato paste. I froze most if it rather than canning. That made sense to me, since even the smallest jars hold more tomato paste than I reasonably will use in one recipe, and I'd end up freezing the unused portions those jars, anyway. Might as well just freeze it from the start.
If you're canning tomato paste, you need to add extra acid - either citric acid powder or lemon juice, according to one of my canning books. So check out a reliable source for the proper amount to add, and the canning time and techniqe. But if you're freezing, you don't need to add anything you don't want to. In my case, I didn't want to add much at all.
Making the tomato paste is easy, but it takes quite a bit of time, and it spends a lot of time on the stove, so it's best to tackle the process on a cool day. You can make as much or as little as you like, and you can season with garlic or bay leaves, or add red bell peppers or even some hot peppers.
Or, as I did, leave it plain. I figure that if I want the taste of garlic or bay in a dish, I can add it separately. But if I don't want those flavors an they're already in my tomato sauce, I can't take it out.
(for the freezer)
Yes, that's really all I used.
Figure that your sauce will be about 1/4 the volume of your tomatoes - or less, depending on how watery the tomatoes are and how thick you want your sauce. Considering you'll spend quite a bit of time babysitting this on the stove, you might as well make enough to make it worthwhile.
Quarter and core your tomatoes, adding them to your heavy-bottomed pot as you finish them. Heat on medium heat, mashing the tomatoes down to break them up. When all of the tomatoes have been added to the pot, add just a bit of salt - figure no more than 1/2 teaspoon to 4 quarts.
Let the tomatoes simmer, stirring occasionally for about an hour, until they are very soft.
Strain the tomatoes through a food mill, strainer, or similar device to remove the seeds and skins from the pulp and juice.
Return the pulp and juice to the pan and continue cooking until the mixture has reduced to the thickness of tomato paste. Because, after all, that's what you're making. This will take 2-3 hours. Don't be tempted to raise the heat too much, or you could burn the sauce. Stir as needed. As the mixture thickens, you will need to stir more often.
When the paste is thick enough, remove it from the heat, let it cool off, then chill it. Freeze in your preferred containers, or scoop it into ice cube trays to freeze, then put the cubes into a zip-top bag to store in the freezer.