COOK PASTRY: Heat the oven to 200°C / 400°F / Gas 6 and line an oven tray with baking paper. Place the butter in a medium saucepan with 150ml of water and bring to the boil. When the butter has melted and the water is at a rolling boil, remove from the heat, add the flour and salt all in one go, then beat with a wooden spoon until the dough is smooth and comes away from the sides of the pan.

ADD EGGS: Allow to cool for 2-3 minutes, then add the eggs a little at a time, beating well between each addition. It may look like the dough is lumpy and nothing is coming together, but if you persevere the pastry will end up smooth and glossy.

PIPE PASTRY: Transfer the pastry dough to a piping bag fitted with a wide 1.5cm star or round tip (see notes) and pipe ten lines of pastry 10-12cm long on the prepared tray, leaving space for the pastry to expand as it cooks. Use a damp finger to press down any peaks of pastry.

BAKE PASTRY: Bake in the preheated oven for 25-30 minutes, until the piped eclairs are golden brown, crisp and well risen. Turn off the oven, remove the tray and use a sharp knife to cut a small slit in the side of each eclair. This allows any steam trapped inside to escape. Return to the oven for 5 minutes to dry out, then remove from the oven and allow to cool completely on a wire rack.

MAKE PASTRY CREAM: While the eclairs are in the oven, make the raspberry pastry cream. Heat the milk and vanilla extract in a medium saucepan until small bubbles are forming around the edge of the pan and the milk is steaming. Meanwhile, whisk together the egg yolks, sugar and cornstarch/cornflour in a small heatproof bowl. Splash a little of the hot milk onto the egg mixture and whisk well, then beat in the remaining milk.

CHILL PASTRY CREAM: Return the mixture to the saucepan and cook, stirring constantly until the mixture thickens. Remove from the heat and beat in the butter, then scrape the mixture into a bowl. Cover with clingfilm, pressing the cling film directly onto the surface and chill in the refrigerator.

FILL AND GLAZE ECLAIRS: When the pastry cream is completely cool, stir through the crushed raspberries, then fill into a piping bag. Use a serrated knife to cut the eclairs in half and pipe the pastry cream onto the bottom half. For the white chocolate topping, melt the white chocolate in a heatproof bowl set over simmering water. Carefully dip the top of the eclairs into the white chocolate, shake off any excess, then place on top of the eclair base.

DECORATE ECLAIRS: Decorate with pistachios and raspberries, then transfer to the fridge for 1 hour to set. Eclairs are best eaten on the day they are made but do keep for a day or two.