Instructions

1. Look at what is in the sauce before you start. A plain tomato sauce dries and keeps well; one with meat, cream or a lot of oil in it does not, because fat cannot be dried out and will turn in the jar.
2. Simmer the sauce down in a pan first until it is noticeably thicker than you would serve it. Every bit of water you boil off is time you are not spending on the machine.
3. Line the trays with parchment paper and spread the sauce thinly with the back of a ladle, no deeper than a few millimetres. A thick pour skins over on top and stays wet underneath, which is how a batch ends up mouldy in a sealed jar.
4. Dry at 135 °F for 5 hours. Break the sheet up and turn it over about two-thirds of the way through, because the side against the parchment paper is always the last to finish.
5. It is ready when the pieces snap rather than bending and nothing feels tacky between your fingers once cooled. Give it another hour or two if any piece is still flexible.
6. Grind the cooled shards to a powder in a blender. Grinding while warm puts steam into the jar, and tomato powder cakes into a solid block the moment it gets damp.
7. Store the powder in a vacuum bag or a sealed jar in the dark and use it within six months. It stays safe for longer than that but the color goes brown and the flavor flattens, and the dried herbs in it fade first.
8. To bring it back, whisk the powder into a pan of water a little at a time and simmer it until it thickens. Swap some of the water for cream or coconut milk if you want it richer, and add cheese at the end off the heat.