Begin by combining the sugar and water over a medium heat until dissolved. Remove from the heat and add in the lemon juice and zest, plus the Thai basil and allow to cool and infuse for at least an hour. Remove the Thai basil leaves and transfer to an ice cream machine for 45-50 minutes or place in a container in the freezer for a minimum of 2 hours. Serve once frozen.
I like to freeze the lemon halves and use them to serve the lemon sorbet in as this helps keep the sorbet from thawing.