Preheat the oven to 210'C.
Cut the butter into small pieces. Sift the flour.
Place the water, salt and butter in a saucepan and bring to the boil. Once boiling, remove from the heat and mix in the sifted flour. Return to the heat and mix until the mixture no longer sticks to the bottom of the pan. Transfer to a food processor and beat in the eggs one by one. The mixture should be shiny and smooth and have a dropping consistency.
Place the mixture into a piping bag and pipe small lines about 5 inches long onto a perforated baking tray. Bake for 10 to 15 minutes then reduce the oven temperature to 180'C and continue to cook for a further 10 minutes to dry them thoroughly and make sure they hold their shape.
Cut the vanilla pod in half lengthways and scrape out the seeds. Whisk the cream with the icing sugar and vanilla to soft peaks. Fill a piping bag with the mixture.
Cut along one side of the eclair and fill with the chantilly cream.
Place the double cream and the milk in a saucepan and bring to the boil. Break the chocolate into small pieces and then pour the cream/milk over the top. Whisk until the chocolate has melted and you have a smooth and shiny sauce.
Dip the top of the eclairs into the chocolate sauce and leave to cool.
«Replace the milk and cream with condensed milk for a smoother, more intense flavour.»