Keep the ingredients in the fridge. Build in a highball glass and stir, topping with crushed ice.
Zest all the lemons (with a microplane/grater). Put the zest aside into a container. Juice the lemons. Measure the juice and add equal parts sugar. Add the same amount of sugar again to the zest, mix and leave overnight. Next day combine the zest sherbert with the lemon syrup. Strain off the zest and bottle.