01 - In a small bowl, sprinkle gelatin over the grapefruit juice. Let it bloom for 5 minutes to soften completely.
02 - In a saucepan, combine the cream, milk, sugar, vanilla extract, and grapefruit zest. Heat gently over medium heat, stirring constantly, until sugar is dissolved and the mixture is hot but not boiling.
03 - Remove from heat. Stir in the bloomed gelatin mixture and whisk until fully dissolved and incorporated.
04 - Pour the mixture through a fine mesh sieve into a clean bowl to remove the grapefruit zest, ensuring a smooth and silky texture.
05 - Divide the panna cotta mixture evenly among 6 ramekins or serving glasses, wiping any spills from the rims.
06 - Allow to cool to room temperature, then cover and refrigerate for at least 4 hours or until completely set and firm.
07 - If desired, toss grapefruit segments with 2 tablespoons sugar and let sit for 10 minutes to macerate and release juices.
08 - Top each chilled panna cotta with macerated grapefruit segments and fresh mint leaves just before serving.