Choux pastry: In a saucepan, combine the water, milk, butter, salt and sugar and bring to the boil over a high heat until the butter has completly melted.
Remove the pan from the heat and add the flour, stirring continuously to form a smooth paste.
Return the pan to the heat and stir with a spatula or wooden spoon for approximately a minute until the mixture pulls away from the sides of the pan. (see notes)
Transfer the mixture to a clean bowl to stop the paste from drying out further and beat in the eggs one at a time. Beat the mixture smooth, ensuring each egg is fully incorporated before adding the next.
Preheat oven to 200°C fan / 425°F / Gas 7.
Choux bun piping: Using a piping bag, pipe small walnut-sized shapes 2cm (3/4 inch) apart, onto a baking sheet lined with silicone or baking paper.
Baking: Bake the choux buns for 10 minutes and then open the oven door a crack and leave it ajar. I use a wooden spoon handle to stop it closing entirely. Continue to bake for another 10-15 minutes until light, crisp and golden.
Testing: It is important to make sure the buns are fully baked as underbaked puffs do not keep well. You can check if they are ready by removing one bun from the oven and spliting it in half. It must be hollow and completley dry inside.
Vanilla custard: Place the milk in a saucepan and bring to a boil.
In a large bowl, whisk the sugar, egg yolks, vanilla and cornflour together.
Pour out about a third of the hot milk onto the egg mixture, whisking continuously. Add the rest of the hot milk until well-combined, then return to the pan.
Cook the mixture over a gentle heat, stirring continuously, until the mixture becomes thick and just comes to the boil.
Remove from the heat and add the butter and stir until melted and thoroughly combined.Cover the custard with heat resistant clingfilm or a piece of greaseproof paper, it must be in direct contact to avoid a skin forming as the pastry cools.Leave to cool and then chill before using. Assembly: In a medium bowl whisk the cream until it reaches ribbon consistency. this is where the whisk leaves a trail in the cream behind as you whisk it. It should be nice and firm and hold its shape.
Cut the cooled choux buns in half and spoon or pipe some vanilla custard into each bottom half. Place raspberries on top of the custard and spoon or pipe some of the whipped cream on top. Place the lid of the choux bun on top and either dust with icing sugar or pipe a small amount of cream on top and raspberry to decorate.