For the filling: In a small mixing bowl whisk together the egg yolk with caster sugar, vanilla, cornflour and plain flour until you have a thick smooth paste.
Pour the milk into the paste and whisk until there are no lumps. Transfer this mix to a small saucepan and place it over medium heat until just boiling, whisking all the time.
Once the custard is thick transfer it to a small bowl and cover the surface with cling film and set aside.
For the pastry: In a medium size saucepan place the water, butter and milk. Place the saucepan over medium heat until the butter has melted, once melted increase the temperature and bring the mixture to the boil.
Remove the pan from the heat and tip in the flour all at once and stir vigorously until the dough begins to come away from the sides of the pan.
Return the dough to the heat and “cook out” the flour for 2-3 minutes stirring all the time.
Line a baking tray with baking paper.
Once cooked out remove the dough from the pot and place it into the bowl of a stand mixer fitted with a paddle attachment.
Turn the mixer on to high speed and add the eggs one at a time beating each egg in well before adding the next.
Once the mixture is glossy and smooth transfer it to a piping bag fitted with a 1cm nozzle
Pipe out 5-6cm lengths of the dough onto the lined baking tray and place into a pre-heated oven combi setting 220 °C once the tray goes in the oven adjust the temperature to 200 °C and bake for 20-24 minutes until golden and crisp.
To finish the filling mixture whisk the cream to soft peaks then add the custard to the cream and fold through to combine, place the cream mix in a piping bag and set aside.
Once the e´clairs are baked remove the tray from the oven and place the e´clairs onto a cooling rack to cool. Once cool cut each e´clair in half.
Pipe a generous amount of cream onto the bottom half of the e´clairs and place the tops on. Finish by pouring over melted chocolate or warm chocolate ganache.
Place in the fridge to set for 5 minutes before serving with strong black coffee