Preheat your oven to 400°F (200°C).

In a medium saucepan, combine the water and unsalted butter. Bring to a gentle boil over medium heat.

Once the butter has melted, add the flour and salt all at once, stirring vigorously until the mixture pulls away from the sides of the pan and forms a ball (about 2 minutes).

Remove the saucepan from heat and let the dough cool slightly for about 5 minutes.

Add the eggs, one at a time, mixing well after each addition until the batter is smooth and shiny.

Using a pastry bag fitted with a round tip, pipe small mounds of batter onto a lined baking sheet, about 1 inch apart.

Bake in the preheated oven for 20-25 minutes, or until golden brown and puffed up. Avoid opening the oven door during baking.

Once baked, let the cream puffs cool on a wire rack.

Whip the heavy cream with powdered sugar and vanilla extract until stiff peaks form.

Slice the cooled cream puffs in half and fill them generously with the whipped cream mixture.