How to Make It
In a medium saucepan, stir the sugar with the water and bring to a boil over high heat. Using a wet pastry brush, wash down any sugar crystals from the side of the pan. Cook, without stirring, until a deep amber caramel forms, about 8 minutes. Remove the saucepan from the heat and carefully whisk in the heavy cream, butter and vanilla bean and seeds. Carefully scrape the caramel sauce into a heatproof glass jar and let cool to room temperature. Discard the vanilla bean.
Spoon 2 tablespoons of the cookie crumbs into each of 4 tall 10-ounce glasses. For each sundae, top the crumbs with a 1/4-cup scoop of the passion fruit sorbet, 2 tablespoons of the caramel sauce and a 1/4-cup scoop of the vanilla ice cream. Repeat the layering once more, starting with the cookie crumbs. Sprinkle 1 tablespoon of the crumbs over each sundae and serve at once.