01 - Sprinkle gelatin over grapefruit juice in a small bowl. Let stand for 5 minutes until gelatin absorbs liquid and softens.
02 - Combine cream, milk, sugar, vanilla extract, and grapefruit zest in a saucepan. Heat over medium heat, stirring constantly, until sugar dissolves completely and mixture is hot but not boiling.
03 - Remove saucepan from heat. Add bloomed gelatin mixture to hot cream, stirring continuously until gelatin dissolves completely.
04 - Pour mixture through a fine mesh sieve into a clean bowl to remove grapefruit zest, ensuring a smooth, creamy texture.
05 - Divide panna cotta mixture evenly among 6 ramekins or serving glasses.
06 - Let cool to room temperature, then cover and refrigerate for at least 4 hours until completely set and firm.
07 - Toss grapefruit segments with 2 tablespoons sugar. Let stand for 10 minutes to macerate and release natural juices.
08 - Top each chilled panna cotta with macerated grapefruit segments and fresh mint leaves. Serve immediately.