Add sugar to water in saucepan; bring to boil. Add mint; simmer 10 minutes. Allow mixture to cool, then refrigerate 10 to 12 hours. Strain out mint and discard. Stir in lemon juice. Process in an ice cream machine according to manufacturers's instructions. Garnish each serving with a sprig of mint if desired. Serves 4. Note: This sorbet will not be particularly green. If you feel that something is missing, add a drop or two of green food colouring.