Heat the oven to 425°F (220°C) and line a baking sheet with parchment paper. Place the water, butter, and salt in a saucepan and bring the mixture to a full boil over medium heat, making sure the butter has completely melted.

Remove the saucepan from the heat and add the flour all at once. Stir vigorously until the ingredients form a smooth dough with no visible dry flour.

Return the pan to medium-low heat and stir the dough for 1–2 minutes. It should pull away from the sides of the pan, and a thin film should form on the bottom.

Transfer the dough to a mixing bowl and let it cool for 5–10 minutes. Beat in the eggs one at a time, mixing thoroughly after each addition; add the final egg gradually because you may not need every last portion.

Pipe or spoon the dough into 12–16 mounds on the prepared baking sheet, leaving space between them. Smooth any peaks with a damp fingertip.

Bake at 425°F for 15 minutes, then reduce the oven to 375°F (190°C) and bake for another 20–25 minutes. The shells should be deeply golden and firm.

Turn off the oven, pierce each puff once with a skewer or knife to release steam, and leave the pastries in the turned-off oven for 5–10 minutes. Transfer them to a rack and cool completely.

Whip the cold cream with the sugar and vanilla until medium-stiff peaks form. Slice the cooled puffs horizontally or make a small hole in the side or bottom, fill them with whipped cream, and dust with confectioners’ sugar.