01 - Combine sugar and water in a small saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Remove from heat and allow syrup to cool to room temperature.
02 - In a large bowl or pitcher, whisk together cooled simple syrup, pink grapefruit juice, grapefruit zest, and lemon juice until fully incorporated.
03 - Transfer mixture to ice cream maker and churn following manufacturer instructions until soft-serve consistency develops, approximately 20-25 minutes.
04 - Spoon churned sorbet into freezer-safe container, cover tightly, and freeze for 4-6 hours until firm enough to scoop.
05 - Portion sorbet into chilled bowls or dessert glasses. Top each serving with 2 fresh basil leaves and serve immediately.