In a large pan, heat the water, butter and salt until the butter has melted. As soon as the liquid boils, tip in all the flour in one go. Remove the pan from the heat and beat vigorously with a wooden spoon until the mixture comes together into a cohesive paste.
Put the pan back on low heat and keep on beating the dough. It should become glossy and come away from the sides of the pan. Take it off the heat and leave to cool down for 10 minutes.
Preheat the oven to 200C Fan. Line a large baking sheet with baking parchment.
Once the dough has cooled down slightly, gradually add the beaten eggs into the dough, beating vigorously after each addition. Keep on adding the egg bit by bit until you have a shiny, thick, pipeable batter that holds shape when piped. When enough egg has been added, it will be thin enough that a large spoonful will fall heavily from the spoon in one lump, but thick enough that it doesn't slide off easily.
Scrape the choux pastry into a piping bag fitted with a 1 1/4 cm plain nozzle. Pipe 10 eclairs (about 10cm in length) on a baking parchment-lined sheets leaving 5 cm in between them, as they will puff up heaps.
Bake in the oven for 10 minutes Wihout opening the door, reduce the temperature to 160C and carry on cooking for another 10 minutes.
Remove the eclairs from the oven and using a sharp knife, pierce a small hole in the side of each eclair to allow the steam to escape. Return eclairs to the oven and bake for another 3-4 minutes to dry them out and crisp up (it's important that you dry them out as you will reintroduce moisture with filling later). Remove the crisp eclairs from the oven and transfer to a wire rack to cool.