I didn't think making sorbet would be this easy. But it is. So try it.

1 c caster sugar
2 1/4 c water
1 1/4 c lemon juice (6-8 lemons)
Rind from 3 lemons
2 egg whites
2 Tbsp limoncello (optional)

Put the sugar and water in a saucepan and stir over medium heat until sugar has melted. Add lemon rind and simmer for 15 mins. Remove rind and stir in liquer if using. Pour mixture into a shallow airtight container and freeze for about 2 hours until mushy. Remove from the freezer and stir.
Whisk the egg whites until stiff peaks form. Fold into the sorbet. Return to the freezer for at least 4 hours, until firm.