Step 1

Preheat oven to 210°C/190°C fan-forced. Lightly grease 2 large baking trays with oil. Combine blueberries, raspberries, strawberries, cornflour and icing sugar in a bowl. Set aside.

Step 2

Place pastry sheets on a flat surface. Cut each sheet into 4 squares. Fold edges over on each square to form a 1cm border. Place on prepared trays. Spoon 1 level tablespoon custard in the centre of each pastry square (don't spread custard). Top with 2 level tablespoons berry mixture.

Step 3

Whisk egg and 1 teaspoon cold water in a small bowl. Using a pastry brush, brush edges of pastry with egg mixture. Bake for 15 minutes or until pastry is golden and puffed. Stand for 5 minutes on trays. Transfer to a wire rack to cool. Serve dusted with icing sugar mixture.