For the pastry, preheat the oven to 180°C. Halve the pastry lengthwise and roll each piece out to a rectangle 2–3 mm (1/8 in) thick. Trim each piece to fit a 20cm x 30cm slice tin. Place the pastry on baking trays lined with non-stick baking paper and sprinkle with caster sugar.

Top each piece with another baking tray as a weight and bake for 10 minutes or until puffed and golden. Cool on racks.

For the filling, place the milk, cream, butter, vanilla and sugar in a saucepan over medium-low heat and cook until hot but not boiling. Mix the cornflour and water to a smooth paste and whisk into the hot milk mixture. Add the egg yolks and stir, allowing to simmer, for 6 minutes or until the mixture has thickened.

Remove from the heat and allow to cool to room temperature. Place one of the pastry sheets in a 20cm x 30cm slice tin lined with non-stick baking paper. Spread over the filling and jam and top with the remaining pastry. Refrigerate for 2 hours or until set.

To serve, dust with icing sugar and slice.