Preheat oven to 200°C/180°C fan-forced. Grease a 6cm-deep, 22cm square cake pan. Line base and sides with baking paper, extending paper 3cm above edges of pan. Grease 2 baking trays. Place 1 sheet of pastry on each baking tray. Bake, 1 tray at a time, for 8 to 10 minutes or until golden and puffed. Carefully flatten pastry. Set aside to cool.

Place sugar, cornflour and custard powder in a heavy-based saucepan over medium heat. Gradually stir in milk until smooth and combined. Add butter. Cook, stirring constantly, for 8 to 10 minutes or until mixture simmers and thickens. Remove from heat. Stir in egg yolks and vanilla.

Place 1 sheet of pastry in base of prepared pan, trimming to fit. Pour hot custard over pastry. Top with remaining pastry sheet, trimming to fit. Set aside for 30 minutes to cool.

Make passionfruit icing Place icing sugar, butter and passionfruit in a heatproof bowl over a pan of simmering water. Stir over heat until smooth and combined. Spread icing over top of pastry. Refrigerate for 4 hours or until cold. Serve cut into squares.