Step 1 In a saucepan, combine the sugar, ginger and water. Heat over medium heat until the sugar is completely dissolved. Strain to remove any ginger fibers, then cool to room temperature.
Step 2 Transfer the mixture to a blender or food processor, add the shiso leaves, lemon juice and egg white and blend until smooth.
Step 3Pour the mixture into an ice cream maker and follow the directions on the machine; alternatively, pour the mixture into a metal container and freeze, scraping the sorbet with a fork every hour or so to break up the ice cream crystals (this will give the sorbet a more granita-like texture).