Prepare a small baking tray (approx. 25x18cm) with high sides by lining with parchment paper. Combine the cornflour and icing sugar together. Dust the baking tray with a layer of cornflour and icing sugar mix. This will stop the marshmallow from sticking.
In a clean saucepan combine the caster sugar, water and glucose syrup. Place over medium heat and stir just until the sugar starts to dissolve. Increase heat to high and leave to cook, without stirring, until the sugar syrup reaches 121°C. Tip: A probe or sugar thermometer will be required and it’s important that you don’t stir the syrup otherwise it may crystallise. Best to use a large saucepan when making the sugar syrup.
Place the egg whites into the bowl of an electric mixer. Ensure the bowl is clean. Start whisking on a low speed when the sugar syrup is at about 118°C.
Meanwhile, soak the gelatine leaves in cold water.
As the sugar syrup approaches 121°C remove from the heat. Remove the soaked gelatine from the cold water and squeeze out any excess water. Add the gelatine to the sugar syrup. Stir until dissolved.
Increase the speed of the mixer to medium then slowly and carefully pour the hot sugar syrup in a constant stream into the egg whites. Add the seeds and pulp of the passionfruit. Continue whisking until the sides of the bowl is cool.
Pour the marshmallow into the prepared baking tray. Dust the surface with icing sugar and cornflour mix. Leave the marshmallow to set at room temperature. Once set, cut the marshmallow into 5cm cubes. Toss each marshmallow in the icing sugar and cornflour mix.