Instructions

1. Cook the peas only until they lose their rawness. Overcooked peas go khaki, and the colour you put on the tray is the best colour you will ever get out of this batch.
2. Put the lemon juice in at the blending stage rather than afterwards. The acid is what holds the green, and stirred in late it only reaches the surface of the puree.
3. Blend the peas, water, lemon juice and cornflour until the puree is as loose as apple sauce with no skins left whole. Pea skins do not break down under a spoon and show up as tough flecks in the sheet.
4. Pour a cupful per sheet onto a lined tray and rock the tray gently until the puree finds its own level. Pea puree is thick enough to hold any ridge you leave in it, and a ridge is a wet spot.
5. The first stage is 52 °C, and it runs 11 hours. It has reached the end of that stage when the sheet releases from the liner in one piece without stretching — which most people call done, and which is about half way.
6. Move the sheets onto the mesh rack and carry on at 52 °C for 3 hours. The underside has been sealed against plastic the whole time and is holding most of the water that is left.
7. It is ready when a corner snaps instead of folding and the whole sheet feels weightless. A leather that still bends is fine to eat this week but it will not keep, and it is useless for grinding.
8. Break the cold sheets into shards and keep them in a jar with the lid tight for six months. Ground to powder, use it within three — the powder loses its colour and its sweet smell far faster than the shards do.