Preheat the oven to 375°F and prepare two baking sheets by lining them with parchment paper.

In a medium saucepan over medium-high heat, combine the butter, sugar, salt, and 1 cup water. Bring the mixture to a boil, stirring frequently.

Once the mixture is a at a boil, remove from heat and quickly add the flour, stirring vigorously. 

Return to heat and mix until a dough forms that is smooth and starts to pull away from the sides.

Transfer the dough to a stand mixer and allow to cool for 6-8 minutes. 

With the mixer on medium, add the four eggs, one at a time. After the first few eggs, the mixture will look curdled. Don't worry! After the last egg, the mixture will smooth out.

After adding the last egg, use a spatula to scrape down the sides of the bowl. Then beat the dough for an additional 2 minutes.  

Transfer the mixture to a piping bag (tips in the post above!) and pipe 1 1/2 inch rounds on the prepared baking sheets. 

Whisk together the last egg with the 1 tbsp of water to make an egg wash. Brush the egg wash on top of the dough mounds. 

Bake for 30 minutes, or until the choux has puffed up and is golden brown all over. You can test a puff by cutting it open. It should be dry and hollow in the center. 

Transfer the puffs to a cooling rack.

Poke a hole in the bottom of each puff (you can use a skewer, cake tester, knife, or piping tip) to allow the steam to escape. 

Once the puffs are cooled, you can fill them with cream.