Scoop out passion fruit juice and seeds. Using a sieve, remove the seeds and reserve the juice.
Add sugar to juice and whisk thoroughly until sugar is dissolved. Divide the juice in half.
Pour one half of the juice in an ice tray and freeze overnight. These will be the passion fruit ice cubes for the mojito.
Cook and reduce the other half of the juice until it reaches a thick texture. Cool completely.
Add mint leaves and sugar to a cocktail shaker and use a muddler to gently muddle the ingredients.
Add the ice, lime juice, passion fruit syrup and white rum. Shake until cold and frothy. Fill 4 mason jars or cocktail glasses with the passion fruit ice cubes.
Evenly divide and pour the passion fruit mojito into the glasses and top each with soda water. Garnish with additional mint. Enjoy!
The passion fruit syrup and ice cubes can both be made up to 4 days in advance.