Preheat the oven to 425° Cover baking sheets with parchment paper.
Add butter, salt, sugar, and 1 cup of water to a medium saucepan. Turn the heat to medium-high. Let come to a boil and quickly add in the flour, stirring with a wooden spoon. Stir continuously until a film appears on the bottom of the pan.
Remove from heat and pour into a bowl. Allow cooling for approx. 4 min. After cooled, stir in 4 eggs, one at a time, incorporating each completely.
Fill a pastry bag with the dough, attaching a 5/8- inch plain icing tip.
Pipe 2-inch rounds onto the baking sheet. If there are peaks on the tops of the rounds, gently smooth them down with a moistened finger.
Whisk the remaining egg together with the teaspoon of water to make the wash. Brush gently over the tops of the pastry rounds.
Bake for 15 min. on the center rack of the oven then reduce oven to 375° and continue baking for approx. 20 min. or until golden brown. Turn the oven off and place the handle of a wooden spoon between the oven and the door to prop open. Keep the cream puff shells in the oven until the oven has cooled to just warm. Remove puffs to a wire rack to cool completely.