the oven to 350 degrees Fahrenheit. Set up two racks to divide the oven into thirds, then preheat it to 350 degrees.

Slice the tomatoes into fourths. tomato slices in fourths.

Olive oil and tomatoes are simmered together. Place the olive oil in a large pot over medium-high heat until shimmering. Tomatoes should be added and cooked until tender and the peels start to separate from the tomato flesh.

Use a food mill to process the tomatoes. Push the warm tomatoes through a food mill, sieve, or chinois to separate the tomato pulp from the seeds and skins. The pulp should be mixed with sea salt and lemon juice or citric acid. Discard or compost the seeds and skins.

Put the pulp on two baking trays. The tomato pulp should be divided between 2 sizable, rimmed baking sheets. You can also use a large roasting pan, but it will take longer to cook down that way.

Bake the tomato pulp until reduced to a paste. In the oven, put the baking sheets. Check the tomatoes every half hour, stirring the paste and altering the position of the baking sheets so that they decrease evenly. Over time, the paste will start to diminish to the point where it doesn’t fill the baking sheet any more. At this point, merge the contents of the two baking sheets into one and continue to bake.

Bake for a reduction of at least 50%. The paste is done when shiny, brick-colored, and reduced by more than half, 3 to 4 hours, though exact baking times will depend on the juiciness of your tomatoes. There shouldn’t be any remaining water or moisture separating from the paste at this point.

Transfer the paste into jars. Divide the resulting paste into 4-ounce jars, leaving 3/4-inch headspace.

Preserving Option 1 – Process the tomato paste in a hot water bath. Apply lids and rings and process in a boiling water bath for 15 minutes. For up to a year, keep in a cool, dark place. After opening, refrigerate for up to 1 week.

Option 2 for preservation: Freeze or refrigerate. If you don’t want to process the paste, you can chill or freeze it instead. Paste should be scraped into tidy half- or quarter-pint jars. Place a layer of olive oil on top of each jar before putting it in the freezer or refrigerator. It will keep in the refrigerator for 3 to 4 weeks as long as you keep it well-covered with olive oil and make sure you only take it out of the jar with a very clean spoon. It can be frozen and kept for up to nine months.