01 - Sprinkle gelatin over grapefruit juice in a small bowl. Allow to bloom for 5 minutes until softened.
02 - Combine cream, milk, sugar, vanilla extract, and grapefruit zest in a saucepan. Heat gently over medium heat, stirring constantly, until sugar dissolves and mixture is hot but not boiling.
03 - Remove saucepan from heat. Stir in bloomed gelatin mixture until completely dissolved.
04 - Pour mixture through a fine mesh sieve into a clean bowl to remove grapefruit zest for a smooth, silky 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 or until completely set.
07 - Toss grapefruit segments with 2 tablespoons sugar if desired. Let sit for 10 minutes to macerate slightly.
08 - Top each chilled panna cotta with macerated grapefruit segments and fresh mint leaves. Serve immediately.