How to Make It
Light a grill. Grill the vanilla beans over high heat until lightly charred, about 1 minute per side. Coarsely chop the vanilla beans, then puree them in a blender with the water and sugar. Pass the vanilla mixture through a fine strainer set over a medium bowl.
In a small bowl, whip the egg white until frothy. Fold the egg white into the vanilla mixture, then pour the mixture into an ice cream maker and freeze according to the manufacturer's instructions. Transfer the sorbet to an airtight container and freeze. Serve the sorbet in bowls; scoop the seeds and pulp from the passion fruit onto the sorbet. Serve immediately.