In a medium saucepan, combine the water, butter, sugar, and salt over medium-high heat.
Cook until the butter is melted, then bring to a full rolling boil over high heat.
Add the flour all at once and stir with a sturdy wooden spoon until everything comes together in a clump that is like a thick paste that cleans the sides of the pan.
Remove from the heat and stir in the eggs, one at a time. The mixture may seem to break or curdle at first, but keep stirring and it will come back together by the time you add the last egg. Let the choux pastry cool for 15 minutes.
Preheat oven to 400 degrees F.
Fill a piping bag with a large round tip with the choux pastry and pipe 12 large puffs, each using about ¼ cup of the choux pastry, onto a parchment lined baking sheet. Dab your finger in water and press down any points on top.
Bake for 35 to 45 minutes until golden brown. Turn off the oven and crack open the oven door to let the cream puffs cool down slowly for 10 minutes before removing from the oven. This prevents them from deflating.
Beat the cream with the powdered sugar and vanilla, then fold into the pastry cream. Transfer the filling to a piping bag fitted with a large decorative tip.
Split each shell down the middle with a serrated knife, then fill with the pastry cream filling. Top with the other half of the shell and dust with powdered sugar before serving.