01 - Sprinkle gelatin over grapefruit juice in a small bowl. Let stand for 5 minutes until gelatin absorbs the liquid and becomes gelatinous.
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 the bloomed gelatin mixture to the hot cream, whisking continuously until gelatin dissolves fully.
04 - Pour the mixture through a fine mesh sieve into a clean bowl to remove grapefruit zest, ensuring a silky smooth texture.
05 - Divide the panna cotta mixture evenly among 6 ramekins or serving glasses.
06 - Allow to cool to room temperature, then cover with plastic wrap and refrigerate for at least 4 hours until completely set.
07 - Toss grapefruit segments with 2 tablespoons sugar in a small bowl. Let sit for 10 minutes to macerate and release juices.
08 - Top each chilled panna cotta with macerated grapefruit segments and fresh mint leaves. Serve immediately.