01 - Combine sugar and water in a small saucepan over medium heat. Stir continuously until sugar completely dissolves. Remove from heat and allow syrup to cool to room temperature.
02 - Whisk cooled simple syrup with pink grapefruit juice, grapefruit zest, and lemon juice in a large bowl until thoroughly combined.
03 - Pour mixture into ice cream maker and churn according to manufacturer's instructions until soft-serve consistency forms, approximately 20–25 minutes.
04 - Transfer sorbet to freezer-safe container. Cover tightly and freeze for 4–6 hours until firm enough to scoop.
05 - Scoop sorbet into serving bowls or glasses. Place 2 fresh basil leaves atop each portion. Serve immediately.