Cut all of the lemons in half and squeeze the juice – you should end up with about 225ml/8fl oz of juice. Boil for 2 minutes and then remove from the heat.įinely grate the zest from 3 of the lemons and add to the sugar syrup. Bring slowly to the boil, stirring to dissolve the sugar. Tip the caster sugar into a saucepan and add 250ml water.