Step 1

Sift self-raising flour, plain flour, custard powder and sugar into a large bowl. Rub butter into flour mixture until mixture resembles fine breadcrumbs. Make a well in centre. Combine egg and 1/4 cup milk in a jug. Add egg mixture to flour mixture. Stir until a soft dough forms. Place on a floured surface. Knead for 30 seconds or until just smooth. Shape dough into a disc. Cover. Refrigerate for 30 minutes or until firm.

Step 2

Preheat oven to 200°C/180°C fan-forced. Grease a 3cm-deep, 20cm x 30cm lamington pan. Line with baking paper, allowing a 2cm overhang at long ends.

Step 3

Roll two-thirds of pastry out between 2 sheets baking paper into a 24cm x 34cm rectangle. Line base and sides of prepared pan with pastry. Spoon apple into pastry case. Roll out remaining pastry between baking paper to a 20cm x 30cm rectangle. Place over apples. Press edges to seal. Brush top with remaining milk. Bake for 40 minutes or until golden. Cool for 15 minutes. Remove from pan.

Step 4

Meanwhile, make icing Sift sugar into a bowl. Stir in butter and passionfruit pulp until smooth and thick. Spread over cake. Set aside for 20 minutes to set. Serve.