180ml (about 10 passionfruits) strained passionfruit juice
20g powdered gelatine
500g caster sugar
snow sugar (see note)
1. Lightly grease and line a 17.5cm x 25cm shallow cake pan and dust base liberally with snow sugar. Combine passionfruit juice and gelatine in a bowl and set aside.
2. Combine caster sugar and 1 cup water in a saucepan and cook over low heat, stirring, until sugar dissolves, then increase heat to medium and cook for 5-10 minutes or until syrup reaches 125C on a sugar thermometer. Remove from heat, add passionfruit mixture to syrup and stir until gelatine dissolves. Meanwhile, using an electric mixer, whisk eggwhites and a pinch of salt until frothy. Gradually add passionfruit mixture, whisking continuously on medium speed until mixture has doubled in size, then slowly decrease speed and mix until mixture is warm (about 40C). Pour into prepared cake pan, and, using a lightly oiled spatula, spread evenly, then dust top liberally with snow sugar. Stand at room temperature for 3 hours or until firm. Using a sharp knife, cut marshmallow into 2.5cm squares and roll in snow sugar to coat. Store in an airtight container between sheets of baking paper at room temperature for up to 2 weeks.
Snow sugar is a confectioners sugar with a vegetable fat added to prevent the sugar from absorbing moisture and dissolving. It’s available from specialty food stores.