Prepare the Dough: In a medium saucepan over medium heat, combine water, butter, salt, and sugar. Heat until the butter is fully melted and the mixture starts to simmer. Reduce the heat to low and add the flour all at once, stirring continuously with a wooden spoon until the dough forms a smooth ball and pulls away from the sides of the pan.

Cool and Add Eggs: Remove the dough from heat and let it cool for about 5 minutes. Add eggs one at a time, mixing well after each addition, until the dough is smooth, glossy, and thick enough to hold its shape when piped.

Pipe and Bake: Preheat the oven to 200°C (390°F) and line a baking sheet with parchment paper. Transfer the dough to a piping bag fitted with a round tip. Pipe small mounds onto the baking sheet, leaving space between each. Bake for 20-25 minutes, or until golden brown and puffed. Avoid opening the oven door while baking. Turn off the oven and leave the pastries inside with the door slightly open for a few minutes to prevent deflation.

Fill and Serve: Once cooled, cut open and fill with pastry cream, whipped cream, or any desired filling. Dust with powdered sugar or drizzle with chocolate before serving.