Method

• 1.
  Toss lemon, sugar and limoncello in a bowl to coat. Cover with plastic wrap and set aside overnight at room temperature.
• 2.
  The next day, strain lemon mixture through a fine sieve into a bowl, squeezing the lemon slices to extract all the juice.
• 3.
  Place 1L (4 cups) of the juice in a blender (add water to make to 1L if necessary). Add glucose and eggwhite, and whiz for 30 seconds or until mixture is well combined and frothy.
• 4.
  Transfer to an ice cream machine and churn according to the manufacturer’s instructions until thick but soft enough to spoon into a container. (Alternatively, pour into a shallow container and freeze for 2 hours or until frozen at edges. Remove from freezer and beat with electric beaters. Return to container and refreeze. Repeat 2 or 3 times.) Transfer to a 1.25L (5-cup) container and freeze for 4 hours or until firm.
• 5.
  To serve, scoop the sorbet into lemon halves, if using, or chilled bowls. Serve immediately.