In a medium-sized saucepan, add the water, melted butter, 1 tablespoon of sugar, and the salt, and cook on medium heat until boiling point is reached.
As soon as a rolling boil is reached, turn off the heat, and add flour all at once. Start to mix with a stiff spatula. The finished texture will eventually look like "mashed potatoes."
Once the "mashed potato" texture is reached, turn heat back on medium, and continue mixing on medium heat for 1 minute.
Crack the eggs into a bowl, and mix with a fork.
Add the eggs to the "mashed potato" mixture in 2 steps. Add the eggs, and mix until the eggs disappear into the dough. Repeat the same steps until all of the eggs are incorporated. Your dough (pâte à choux) is ready when it is smooth and shiny.
Pipe the cream puffs onto a nonstick baking tray or silicone mat.
Bake for 30 to 40 minutes (depending on the size). Then, set them aside to cool down.
In a large bowl, add the cold heavy whipping cream, 2 tablespoons of sugar, and vanilla flavor (bean or extract), and whip on medium speed. Gradually work up to high speed until thick.
Make a small hole in the bottom of the cream puffs with the tip of a knife.
Add the vanilla whipped cream to a pipping bag, and fill the cream puffs.