Preheat the oven to 200°C / 400°F / Gas 6. The pastry forms the base and the lid of the custard squares, so roll out the pastry to two equal sized pieces slightly larger than your baking tin, roughly 22 x 32 cm.

Put the pastry pieces on a baking paper lined oven tray, prick really well all over with a fork, and bake in the preheated oven for 15 minutes until golden brown. Remove from the oven, gently squash each piece slightly and allow to cool on wire racks.

Meanwhile, prepare your custard by combining the cream, milk, sugar, butter and vanilla in a medium saucepan. Stir over a medium heat until the sugar is dissolved and the butter is melted. Do not allow the mixture to boil, you should be able to hold your little finger in the liquid comfortably. When you see tiny bubbles forming around the edge of the saucepan, remove it from the heat.

Whisk together the water and the cornflour, ensuring there are no lumps, then pour into the cream, whisking well as the mixture thickens. Pour in the beaten egg yolks, return to the heat and continue whisking over a low heat for two to three minutes until the mixture is very thick. The custard has to be thicker than normal so that it sets fairly solid when cooled. Make sure you get into the corners of the pan with the thick so that the custard doesn't catch.

Remove from the heat and allow to cool slightly, stirring from time to time to get rid of any lumps.

Line a 20 x 30cm dish (ideally deep, with straight sides) with baking paper, leaving an overhang as a 'handle', and place one of the pastry pieces on the bottom, trimming with a sharp knife if necessary to fit. Pour over the warm custard, then top with the second pastry piece, pressing down gently to settle the custard.

Place in the refrigerator and allow to chill for a minimum of two hours. It's important that the custard completely sets so give it plenty of time to chill.

When the custard is set, remove from the fridge, dust liberally with icing sugar, slice and serve. It is easiest to use the tip of a long sharp knife to cut downwards through the first pastry layer before slicing completely through. Delicious on it's own or with fresh raspberries to serve.