In a medium saucepan, combine the water, unsalted butter, and salt. Bring this mixture to a boil over medium heat, allowing the butter to melt completely.
Once the mixture is boiling, remove it from heat and quickly add the all-purpose flour. Stir vigorously with a wooden spoon until the dough comes together and pulls away from the sides of the saucepan, creating a smooth ball.
Let the dough cool for a few minutes. Then, add the eggs one at a time, mixing well after each addition. The dough should become smooth and glossy.
Preheat your oven to 400°F (200°C). This high temperature is crucial for the choux pastry to puff up beautifully.
Transfer your dough to a piping bag fitted with a round tip. Pipe small mounds onto a baking sheet lined with parchment paper, leaving space between each mound as they will expand while baking.
Bake the pastries in the preheated oven for 20-25 minutes, or until they are golden brown and puffed. Avoid opening the oven door during the first 15 minutes of baking to maintain the heat.
Once baked, remove the choux pastries from the oven and let them cool completely on a wire rack. Once cool, fill them with your choice of cream, custard, or mousse using a piping bag.