1.Beat butter and sugar in small bowl with electric mixer until just combined; beat in egg. Stir in sifted flours, in two batches. Turn dough onto floured surface; knead until smooth. Cover; refrigerate 30 minutes.
2.Meanwhile, make filling. Sprinkle gelatine over milk in small jug. Blend sugar and cornflour with extra milk in small saucepan; stir over heat until mixture boils and thickens, remove from heat.
3.Quickly stir in egg yolks, then gelatine mixture; stir until smooth. Divide custard into two bowls. Stir chocolate into one bowl. Cover both bowls; cool to room temperature.
4.Stir extract into plain custard. Beat egg whites in small bowl with electric mixer until soft peaks form; gradually add extra sugar, beating until dissolved after additions. Fold egg white mixture into vanilla custard, in two batches.
5.Preheat oven to 200°C/400°F. Roll pastry on floured surface until large enough to line 24cm (9½-inch) pie dish. Ease pastry into dish, press into base and side; trim edge. Prick pastry all over with fork.
6.Bake pastry case about 15 minutes or until browned; cool.
7.Spread chocolate custard into pastry case; refrigerate until firm. Spread vanilla custard into pastry case; refrigerate until firm. Spread whipped cream over custard, then sprinkle with grated chocolate.