4 juicy lemons
125g/4oz/½ cup caster (superfine) sugar
2–3 tbsp limoncello
1 large (US extra-large) egg white
1 Finely pare the lemon zest, then squeeze the juice. Put the zest in a pan with the sugar and 350ml/12fl oz/1½ cups water and heat gently, stirring until the sugar dissolves. Increase the heat and boil for 10 minutes. Set aside to cool.
2 Stir the lemon juice and limoncello into the cooled sugar syrup. Cover and chill in the refrigerator for 30 minutes.
3 Strain the syrup through a fine sieve into a bowl. In a clean, dry bowl, beat the egg white until just frothy, then whisk into the lemon mixture.
4 Freeze in an ice-cream maker and follow the instructions. If you don’t have one, pour into a shallow freezerproof container and freeze until almost frozen. Remove and mash well with a fork, then freeze until solid.
5 Transfer the sorbet to the refrigerator 30 minutes before serving to soften slightly.