1. Preheat the oven to 425°F (210°C).
2. Place the water, butter, sugar and salt in a medium sized saucepan and place on medium heat. Remove from heat as soon as the butter has melted and the water is boiling.
3. Using a wooden spoon, stir in all of the flour at once. Mix for at least two minutes and until the mixture is smooth, detaches from the sides of the pan, and forms a ball. The residual heat of the pan dries the dough as you are stirring.
4. Add one egg and beat the mixture vigorously with a wooden spoon until the egg is fully incorporated. Add the other three eggs, one at a time, in the same fashion. Each egg takes about a minute to be absorbed into the batter.
5. You can use a pastry bag to form the pastries, or work with two spoons (one to scoop the batter and the other to slide it off the first spoon onto the tray). If you use a pastry bag, a 1/2 inch diameter tip is good for small puffs and a 3/4 inch diameter tip is good for large puffs. When forming the puffs, keep in mind that each one will at least double in size in all directions.
6. Scoop or pipe the puffs onto a baking tray covered with parchment cooking paper. If you wish, use a pastry brush to lightly coat the tops of the puffs with beaten egg. This will give the puffs a lovely shiny and slightly crunchy finish.
7. For small puffs, bake at 425°F (210°C) for 20 minutes. For larger puffs, after 20 minutes of baking, lower the oven temperature to 375° F (190°C), and bake 10 to 15 minutes longer. To insure that the inside of the choux pastry does not get soggy after baking, pierce each puff and return the tray to the oven that has been turned off. Leave them in the oven with the door ajar for 10 minutes.

This makes about 2 cups of choux paste, good for 40 small puffs or 12 larger ones.