Homemade Tomato Paste

Ingredients

• 10 pounds very ripe plum or salad tomatoes, cored
• 1 to 4 tablespoons kosher salt, depending on personal preference
• 1 tablespoon extra-virgin olive oil for the baking sheet, plus more for topping off the jar

Directions

1. Before you begin, know that the finished paste depends almost entirely on the tomatoes you start with. Choose fully ripe, aromatic summer tomatoes, ideally from a farmers market or garden; standard supermarket tomatoes are not worth the effort here. San Marzano tomatoes work beautifully, but any ripe plum tomato or salad tomato is fine.
2. For plum tomatoes, slice them lengthwise through the center. For larger round tomatoes, quarter them. Use your fingers to scoop out the seeds, then put the tomatoes into an 8-quart stainless steel pot. Bring them to a boil, stirring now and then, until they give off their liquid. Continue at a lively boil for 30 minutes, until the tomatoes are tender and the liquid has cooked down.
3. Run the cooked tomatoes through a food mill with the fine disk in place, leaving the skins and any seeds behind.
4. Pour the tomato purée back into the same pot and place it over high heat. Add the salt, lower the heat to mediumish, and cook at a simmer, stirring often, until the purée is reduced to about 1 quart (4 cups), 45 to 55 minutes. As it gets thicker, lower the heat as needed so it does not bubble up wildly and splatter.
5. Coat a 12-by-17-inch rimmed nonaluminum baking sheet lightly with oil. Spread the thickened tomato purée across it with a rubber spatula in a smooth, even layer, covering the whole sheet.
6. Heat the oven to 200ºF (93ºC), using the convection fan if your oven has one. Set a rack in the center.
7. Slide the baking sheet into the oven and bake for 30 minutes.
8. Take the sheet out of the oven, but leave the oven on. Stir the purée with the rubber spatula so it dries consistently and does not develop a crust, then spread it back out into a rectangle about 1/8 inch thick. Be meticulous here, since thin spots can burn. The purée will have shrunk and will no longer fill the pan. Wipe away any tomato clinging to the edges or uncovered areas of the baking sheet with a paper towel.
9. Put the baking sheet back in the oven and keep baking until the purée has changed from saucy to very thick, firm, and slightly tacky, about 3 more hours. Every 20 minutes, stir it and spread it out carefully again the same way. The rectangle will keep getting smaller as moisture cooks off. Taste it, and add more salt if you want.
10. Cool the tomato paste to room temperature.
11. Spoon the paste into a clean jar, pressing it down so no air pockets remain. Smooth the top with the back of the spoon. Pour in enough olive oil to completely cover the surface, with no paste exposed. Screw on the lid and refrigerate. It will keep in the refrigerator for at least a year.
12. Use this homemade tomato paste by the teaspoon when you want to build depth in a dish. Since it carries a good amount of concentrated saltiness, wait to adjust the salt in the dish until after the paste has gone in. Whenever you take some from the jar, smooth the surface again and add more oil so the remaining paste is fully submerged. Originally published August 27, 2013.