01 - Sprinkle gelatin over grapefruit juice in a small bowl. Let stand for 5 minutes until gelatin absorbs liquid and becomes soft.
02 - Combine cream, milk, sugar, vanilla extract, and grapefruit zest in a saucepan. Heat over medium heat, stirring constantly, until sugar dissolves and mixture is hot but not boiling.
03 - Remove saucepan from heat. Add bloomed gelatin mixture and stir vigorously until completely dissolved into the cream base.
04 - Pour mixture through a fine mesh sieve into a clean bowl to remove grapefruit zest pieces and ensure silky smooth texture.
05 - Distribute strained panna cotta evenly among 6 ramekins or serving glasses. Wipe any spills from rims for clean presentation.
06 - Let panna cotta cool to room temperature uncovered. Cover with plastic wrap and refrigerate for at least 4 hours or until fully set.
07 - Toss fresh grapefruit segments with 2 tablespoons sugar in a small bowl. Let macerate for 10 minutes to release natural juices.
08 - Top each chilled panna cotta with macerated grapefruit segments. Garnish with fresh mint leaves just before serving.