Preheat oven to 180 degrees.
In a saucepan over medium-high heat, combine butter, sugar, salt and 1 cup water. Bring to a boil and quickly stir in the flour with a spoon. Continue to stir until you see a film forms on the bottom of the pan, like 3 minutes.
Remove from heat and let it cool for a bit, about 3 minutes. Add 4 eggs, one at a time, be sure that you incorporate each egg after each addition.
Transfer the pastry puff mix to a large pastry bag fitted with a 5/8-inch plain tip. Pipe 3 cm rounds onto each prepared pan.
Gently press back the pointed peaks with a moistened finger, rounding tops to ensure even rising. Brush tops with reserved egg wash.
Bake until puffs rise and are golden brown, about 30 minutes; do not open the oven till the 30 min is over otherwise the pastry puff will not grow at all.