Prepare the Pâte à Choux Dough:

Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper or a silicone mat.

In a medium saucepan, heat the water and butter over medium heat until the butter is completely melted and the water comes to a boil.

Add the flour and salt all at once. Stir constantly until the dough forms a smooth ball and pulls away from the sides of the pan, about 1-2 minutes.

Remove from heat and let the dough cool for 2-3 minutes. Then, add the eggs one at a time, mixing well after each addition until the dough becomes smooth and shiny. Add the vanilla extract, if using.

Transfer the dough to a piping bag and pipe small mounds (about 1 to 1.5 inches in diameter) onto the prepared baking sheet.

Bake the Puffs:

Bake the cream puffs for 20-25 minutes or until golden brown and puffed up. Avoid opening the oven door during the first 15 minutes of baking.

Once done, turn off the oven and let the puffs cool inside for 10 minutes with the door slightly ajar. Then, remove the puffs and let them cool completely on a wire rack.

Make the Filling:

While the puffs are cooling, whip the heavy cream with the powdered sugar and vanilla extract in a mixing bowl until soft peaks form (about 3-4 minutes).

Fill the Puffs:

Once the cream puffs have cooled completely, carefully cut a small slit in the side of each puff and fill with the whipped cream mixture. You can use a piping bag for a more precise fill or spoon the cream in.