In a small bowl, squeeze the juice from one large grapefruit and sprinkle gelatin powder over it. Allow it to sit for 5 minutes to bloom.

In a saucepan, combine whipping cream, granulated sugar, and vanilla extract over medium heat, stirring until just warmed and sugar dissolves (4-5 minutes).

Remove from heat and stir in the bloomed gelatin mixture until completely dissolved and smooth.

Pour the mixture into ramekins and chill for 2-3 hours, or overnight until set.

Whip the remaining whipping cream in a mixing bowl until soft peaks form; add powdered sugar and whip until combined.

Once set, dollop the whipped cream on top and garnish with grapefruit segments and crushed pistachios before serving.