Make the brine by dissolving the salt in 500ml warm water. Allow to cool while you peel and trim your onions or shallots.
Add the onions to the brine. Use a plate or bowl weighed down with a tin or other heavy object to keep them all submerged, then leave for 24 hours.
Gently heat the vinegar and remaining ingredients in a saucepan until simmering, but not boiling. Remove from the heat and allow to cool completely.
Sterilise your jar by placing it on a tray in the oven for 15 minutes at 180°C, fan 160°C, gas mark 4. Allow to cool.
Once your jar has cooled, drain the onions, rinse and pat dry before packing tightly into the jar.
Pour in the cooled vinegar and spices, completely covering the onions and secure the lid. Keep for at least a month before eating.
*All information included in this recipe has been provided by Aspall.