1.Preheat oven to 240°C (220°C fan-forced). Grease 22cm deep square cake pan; line with foil, extend foil 10cm over sides of pan.
2.Place each sheet on separate greased oven trays. Bake for about 15 minutes; cool. Flatten pastry with hand; place one sheet in pan, trim to fit, if necessary.
3.Meanwhile, in a medium saucepan over medium heat, combine sugar, cornflour and powder; gradually add milk, stirring for 1-2 minutes, or until smooth. Add butter; stir for about 1 minute, or until mixture boils and thickens. Simmer, stirring, for about 2-3 minutes or until thick and smooth. Remove from heat; stir in egg yolk and extract. Cover with plastic wrap; cool.
4.Meanwhile, to make passionfruit icing: Place sugar, butter and pulp in small heatproof bowl over small saucepan of simmering water (make sure the bowl does not touch the water); stir for about 1 minute, or until icing is spreadable.
5.Using an electric mixer, beat cream in a small bowl for about 2 minutes, or until firm peaks form. Fold cream into cooled custard, in two batches.
6.Spread custard mixture over pastry in pan. Top with remaining pastry, trim to fit, if necessary; press down slightly. Spread icing over pastry.
7.Refrigerate slice for 3 hours or overnight before serving.
It’s best to store any leftover slice in large pieces, so if you think it won’t all be eaten or you want to save some for later, keep a portion without cutting it into squares or bars. Keep the piece of slice as airtight as possible in a resealable plastic bag or an airtight container, and cut it just before you’re ready to serve.