Preheat an oven to 80 - 100 degrees c
1. Zest the lemons and mandarins (or equivalent) into a bowl with as new/sharp a grater as is to hand. Take care to be methodical and to grate the rind and not the pith.
2. Line a baking tray with baking parchment so that the parchment bunches up in the corners and comes up around the edges of the tray (this will avoid waste and be useful later).
3. Add the salt to the tray. Combine the zest in the bowl and try to break up any clumps (this is why the sharp grater is helpful). Add the zest to the salt as evenly as possible and mix together with the back of a tablespoon.
4. Place the tray in the oven and bake for 60 - 90 minutes. Give the tray a periodic shake and remove it to smooth around the salt and zest and check for/prevent burning.
5. The salt is ready once it is fully dehydrated and crunches, salt and zest between the fingers. Leave to cool for 10 minutes and then use the baking parchment as a makeshift funnel to transfer to a sealable container
Tips: Cornish Sea Salt Co sell salt that would work well for this recipe in 225 gram containers that may be reused to keep it, perhaps once you've first used a little of the original salt.