For the eclairs, place the butter and water into a pan and bring up to the boil. Once the butter has melted, take the pan off the heat and tip in all the flour. Beat well with a wooden spoon until the mixture comes away from the sides of the pan. Beat in the eggs one at a time until completely incorporated. Stir in the salt. Transfer the mixture to a piping bag and allow it to cool for a few minutes. Preheat the oven to 200C. Pipe 2″ lengths of pastry onto a floured baking sheet. The pastry will at least double in size as it cooks, so give the eclairs plenty of space to expand on the baking sheet. Transfer to the oven and bake the eclairs for about 30-40 minutes, or until golden-brown and firm. Remove from the oven and allow it to cool completely .