Perfect Homemade Tomato Paste, Slow-Cooked in the Sun

This homemade tomato paste is slowly concentrated under the September sun until it takes on a ruby-red color. The recipe presents five techniques for achieving a thick, smooth paste that can last through the winter.

Start with meaty, rather than watery, tomatoes, preferably pear- or egg-shaped varieties. Chop them and sprinkle them with rock salt, then leave them overnight in a deep container or sack. This allows the tomatoes to release their acidic, yellowish liquid, which the recipe identifies as the main secret to a sweeter paste that resists spoilage.

Once the tomatoes have softened, turn them into a purée and pass the mixture through a fine-mesh strainer or tomato mill. Removing every seed helps prevent later fermentation and creates the smooth, silky texture associated with restaurant sauces.

The purée should then go into a wide pot and boil for about one to two hours, until much of its water has evaporated and the mixture thickens. The recipe insists on using only a wooden spoon while stirring. When the paste has reduced by about half, spread it on trays and place it in the sunniest spot on the balcony.

Sunlight deepens both the color and the natural aroma. Stir the paste at least three or four times a day with a wooden spoon so the surface does not form a crust and the mixture dries evenly. It is ready when tilting the tray no longer makes it run. Add more rock salt, press the paste firmly into jars to remove air pockets, and cover the surface with about two fingers' thickness of extra-virgin olive oil.