Rinse and cut tomatoes into quarters. Core them; Roma tomatoes may not need seed removal.

Place the chopped tomatoes in a pot and cook over medium-low heat until they soften and release juices, stirring occasionally.

When they begin to soften and fall apart, increase the heat to medium and let them simmer until reduced by half.

Pass the cooked tomatoes through a food mill or mesh strainer to remove the skins and seeds.

Preheat the oven to 275°F (135°C) and line a large baking sheet with parchment paper or a silicone mat and lightly oil it.

Spread the tomato pulp evenly on the prepared baking sheet to a thickness just under 1/4 inch.

Bake at 275°F for 45 minutes to 1 hour, scraping and redistributing every 20–30 minutes.

Reduce the heat to 200°F (93°C) and continue to cook, scraping and redistributing every hour, until the paste is dark, thick, and looks like paste (about 2–4 hours, depending on the batch).

Let the paste cool, then portion it into freezer-safe amounts (3–6 tablespoons per portion) and freeze.

For refrigerating, keep it in an airtight container with a thin layer of olive oil on top and use it within about 1 month.