First things first, preheat your oven to 200°/180°C Fan/Gas Mark 6. Line a larger baking tray with parchment paper and using a pencil draw 8 12 cm lines spaced apart, this will help guide you when you’re piping your eclairs.
Pop the butter in a saucepan with 150ml of water. Heat gently on a low heat until the butter has melted, then turn up the heat and bring to the boil. Once boiling remove from the heat and immediately mix in the flour, beating well with a balloon whisk until thick, glossy and smooth – the mixture should form a soft ball of dough in your saucepan. Pour your ball of dough into a heatproof bowl and leave to cool for 10 minutes.
Gradually pour in the beaten eggs and whisk well between each addition until you have a thick, glossy mixture, you may not need to add all your egg so keep an eye on the consistency of your mixture.
Your choux pastry is now ready to pipe! Grab your parchment paper your prepared earlier and run under some cold water, allow the excess water to drip off and place back on your baking tray, this will help create more steam in the oven and help your choux puff up even more! Pop your choux pastry in a piping bag fitted with a large star nozzle, the more points your nozzle has the better, if you don’t have a large star nozzle don’t worry you can simply cut a 2 cm hole in the end of your piping bag.
Pipe your choux pastry onto your baking parchment using your lines to help guide you, to get a neat end use a pair of scissor to cut the choux pastry away from the piping bag once you have piped an éclair. Once all your eclairs are piped pop them in the oven and bake for 25-30 minutes until golden in colour and puffed up. Pop on a cooling rack and allow to cool completely.
Whilst your eclairs are baking it’s time to make the filling; sift the flour into a bowl, pop in the cornflour, then mix in the egg yolks and sugar to make a smooth paste. Pop the milk and Vanilla Paste in a pan and bring to the boil, stirring well. Pour half of your boiled milk mixture into your egg yolk mixture and whisk together until smooth. Pour into the remaining milk and heat on a medium heat whisking your mixture until it begins to boil. Reduce the heat and simmer for another 1-2 minutes. Pour into a bowl and cover with cling film, making sure the cling film touches the surface of your custard to stop a skin from forming on the surface. Leave your filling to cool.
Once your filling has cooled, whisk until it’s smooth then pop into a piping bag fitted with a ½ cm nozzle, if you do not have a nozzle don’t worry just cut a small hole off the end of your piping bag.
Make 2 small holes into the base of each éclair and pipe your filling into each éclair to fill them, the filling will come out of the opposite hole when your éclair is full.
To make your chocolate topping, boil your cream in a saucepan. Once it’s boiling pour over your Extra Dark Chocolate broken into pieces in a heatproof bowl. Leave for a minute then stir to until you have a glossy chocolatey mixture. Leave to cool so your ganche thickens slightly.
Now to get your eclairs decorated, pop your chocolate ganache into a piping bag and cut a 1cm hole onto the end of the piping bag. Melt the White Chocolate in the microwave for 30 seconds then melt in 10 second bursts until melted, stir your chocolate well between bursts.
Pipe a line of dark chocolate ganache onto the top of each éclair and then smooth out with a palette knife to cover. Blob the melted White Chocolate onto the ganche and use a cocktail stick to marble the chocolate together!
Now it’s time to tuck in and enjoy your eclairs!