Heat oven to 200°C / 180°C (fan oven) / 395°F / Gas Mark 6. Line a large baking tray with baking parchment. Roll out the pastry on a lightly floured surface and cut into 30 x 6cm squares, trimming any edges. Score a smaller square inside each one, leaving a 7.5mm border, taking care not to cut the pastry all the way through.

Put the squares on the tray, lightly brush with egg glaze and bake for 15 mins until puffed up and golden brown. Transfer to a wire rack to cool. When cool, carefully remove and discard the central piece of pastry from each one. To serve, fill with various fillings, such as mushrooms, egg or trout. The vol-au-vent cases can be kept in an airtight container for up to a day before filling and serving.