Preheat an oven to 218c (425f) and prepare a baking sheet with parchment paper.
In a saucepan, add the butter, sugar, water, and salt, over medium heat, mix with a wooden spoon until the butter is melted and the mixture is well mixed. Bring to a boil.
Add the flour and turn the heat to medium low and stir constantly until you dont see lumps of flour visible and the mixture is well combined. Keep stirring for 1-2 minutes to release extra moisture from the dough.
The dough will come together into a ball and a thin film will form in the bottom of the pan.
Transfer the dough to a large mixing bowl and mix with an electric hand mixer for about 2 minutes to cool down the dough.
Add 4 eggs, one at a time, and let each egg mix thoroughly into the dough. Mix for another minute to let the mixture mix well and be smooth.
Transfer the dough to a pastry bag with a round piping tip and pipe the puffs 1 inch apart.
Bake in a 218c (425f) preheated oven for 10 minutes, then lower the temperature to 180c (350f) for another 30 minutes. The puffs should look golden brown.
Check for doneness by cutting one puff in half. If the inside of the pastry is very moist and spongy, bake for another 2-3 minutes. It is important that the interior of the puffs is not moist. This way they will not deflate.
Let them cool completely before filling them.