Firmer and less watery than other types, paste tomatoes are perfect for canning, cooking, and making intensely flavored tomato paste, which enhances numerous dishes.
Preheat oven to 250 degrees. Heat oil in a large, heavy saucepan over medium heat. Add tomatoes and salt. Cook, stirring occasionally, until the tomatoes have broken down, 5 to 10 minutes.
Pass tomatoes through a food mill or a fine sieve; discard seeds and skin.
Pour sauce evenly onto a rimmed baking sheet. Bake until mixture begins to thicken, about 3 hours. Stir with a rubber spatula to redistribute, and spread evenly on sheet. If tomato mixture no longer fills sheet, transfer to a smaller sheet.
Bake until liquid has completely evaporated and mixture has thickened, about 3 hours more, stirring every 30 minutes.
The tomato paste can be refrigerated in an airtight container up to 3 weeks or frozen up to a year.