Deseed pomegranates. Slice vanilla bean in half and scrape the seeds from the pod.
Add pomegranate seeds, sugar, water, vanilla bean and seeds to a pot and bring to a boil. Reduce heat to low and let simmer for approx. 20 min., stirring occasionally.
Strain grenadine syrup through a sieve. With a rubber spatula, press out juice from pomegranate seeds. Let cool, then transfer to a bottle.
Add some grenadine syrup, gin, passionfruit nectar, and crushed ice in a cocktail shaker. Shake vigorously. Pour the cocktail mixture into a glass, top with ginger ale, and garnish with basil. Enjoy!