Put the ginger in a bowl and add 1 tsp salt, rubbing it all over the ginger. Leave uncovered for 1 hr (this will reduce the fiery heat of the ginger). Rinse off the salt, then pack the ginger and radish slices into a sterilised 150ml jar that has a rubber seal.

Put the sugar, 100ml water, rice wine vinegar and a generous pinch of salt in a pan and bring to a boil, stirring so that the sugar dissolves. Pour this into the jar with the ginger and radish slices, then leave to cool before putting the lid on. Leave to pickle for at least 8 hrs in the fridge. Remove the radishes from the jar. Will keep chilled for a month. Serve alongside sushi.