01 - Combine water and sugar in a small saucepan. Bring to a gentle simmer over medium heat, stirring constantly until sugar completely dissolves. Remove from heat immediately.
02 - Add fresh basil leaves to the hot syrup, pressing gently with a spoon to release essential oils. Cover and steep for 10 minutes to extract flavor.
03 - Pour the infused syrup through a fine mesh strainer into a mixing bowl. Discard used basil leaves.
04 - Whisk in freshly squeezed pink grapefruit juice, grated grapefruit zest, and lemon juice if using. Stir thoroughly until fully incorporated.
05 - Cover the bowl and refrigerate for at least 1 hour until completely cold. Chilling ensures proper texture during churning.
06 - Pour chilled mixture into an ice cream maker. Churn for 20 to 25 minutes following manufacturer instructions until reaching soft-serve consistency.
07 - Transfer sorbet to a freezer-safe container. Cover tightly and freeze for at least 3 hours until firm.
08 - Let sorbet stand at room temperature for 5 minutes before scooping to achieve optimal texture. Serve immediately in chilled bowls.