Combine sugar, zest and salt until smooth. (You can mix with blender)
Add water and juice and beat until sugar dissolves.
Pour the whipped mixture into a container, cover with cling film and
place in the freezer for 4 hours.
Remove lemon ice from the freezer and mix in a blender.
Freeze for another 3 hours, stirring occasionally (once every half an hour or an hour).
