Remove the insides of 2 passion fruits, and squeeze them into a small bowl through a fine mesh sieve with the back of a spoon. Alternatively, if you don't mind a bit of texture, blend the passion fruit insides a blender.

In a cocktail shaker filled with ice, combine passion fruit juice, passion fruit puree, lime juice, vanilla simple syrup. Shake vigorously until fully chilled, about 30 seconds.

Transfer to a chilled martini glass or champagne coupe, and garnish with a passionfruit. Serve with a shot glass of soda water (this is drunk right after the passionfruit martini, as a chaser and palette cleanser).