Preheat the oven to 400°F/204°C. Begin by adding the water, butter, and salt to a saucepan. Place it over medium heat. Bring the ingredients to a boil stirring occasionally.
Remove the pot from the heat and add in the flour all at once and stir quickly until a nice dough forms.
Place the dough in a bowl and continue to stir the dough until it becomes warm to the touch. Then add in one egg and stir it in. It will seem like it doesn't want to combine at first, but it will, stir until completely combined.
Add the choux pastry to a pastry bag or zip lock bag with a round tip. Pipe the pastry onto a parchment paper-lined cookie sheet or sheet pan using a circular motion to create a little mound.
Bake the choux pastry mounds in the oven for 15 minutes. Then turn the oven down to 350°F/176°C and allow them to bake for another 15-20 minutes. (Do not open the oven too soon or it may cause the puffs to collapse or not rise at all.) They should be nice and golden brown on the top when done. Remove from the oven and allow them to cool while you make the sweetened whipped cream.
Sweetened Whipped Cream
In a bowl, combine the heavy cream with the sugar and vanilla extract. Whip it with an electric mixer or by hand until nice stiff peaks form.
Cut the shells in half and scoop the whipped cream in. Dust the tops with powdered sugar and serve.