Instructions

1. Peel the onions and cut off both ends, then check the layers as you slice. A brown or slimy layer anywhere in the middle means the onion is going over and the whole thing is better composted than dried.
2. Slice them into rings about 6 mm thick and shake the rings apart with your fingers. A stack of rings still nested inside one another dries as a solid block.
3. Spread them loosely on the trays and run the machine somewhere other than the kitchen if you can. Onions scent everything in the house, and anything else drying at the same time will taste of them.
4. Dry at 54 °C for 3 hours, checking the trays as you go and pulling off the thin outer rings as they finish. They will be done well before the thick inner ones and they scorch if left.
5. The rings must be brittle rather than leathery — one should shatter when you press it, not bend. This matters more for onion than for almost anything else, because a single pliable ring will turn the finished powder into a solid lump.
6. Let the rings cool completely, then grind them in short bursts. Onion sugars soften under a hot blade and start sticking to the sides of the jug.
7. Leave the grinder closed for ten minutes before you open it. The powder is fine enough to hang in the air, and opening the lid straight away puts most of the batch on your counter and in your eyes.
8. Jar it airtight with a few grains of rice or a desiccant sachet and keep it dark. It holds its flavour for about six months, and the rice is not superstition — onion powder pulls water out of the air and sets like concrete without it.