Preheat oven to very hot, 220 deg Celsius. Lightly grease a 23 cm square cake pan and line with baking paper, leaving a 2cm overhang (see notes)
Line 2 baking trays with baking paper. Bake pastry sheets for 10-12 minutes until golden. Gently flatten pastry with hand. Trim pastry sheets to fit base of prepared cake pan. Lay 1 sheet in pan.
In a medium saucepan, combine sugar, cornflour and custard powder. Combine milk and cream in a bowl. Add a little to the sugar mixture to form a paste. Blend remaining milk mixture into sugar mixture, stirring until smooth.
Add butter and bring to the boil on medium, stirring. Reduce heat to very low and simmer, stirring, for 4-5 minutes until mixture is thick and smooth. Remove from heat. Add egg yolks and vanilla bean paste. Pour over pastry sheet. Top with remaining sheet. Chill for 1 hour.
ICING: Combine icing sugar and butter in a small heatproof bowl. Stir in enough passion fruit pulp to make a smooth paste. Place over a saucepan of simmer water and heat gently, stirring, for 2-3 minutes until mixture is a spreadable consistency. Spread over pastry. Chill for 30 minutes until set. Cut into squares to serve.