1.  Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper. 
2.  Combine water, butter, and salt in a saucepan and bring to a boil. 
3.  Add the flour all at once and stir vigorously until a smooth dough forms. 
4.  Cook for 1–2 minutes, stirring until the dough pulls away from the sides. 
5.  Transfer the dough to a bowl and let it cool slightly. 
6.  Add the eggs one at a time, mixing well after each addition. 
7.  Transfer the dough to a piping bag. 
8.  Pipe small rounds onto the prepared baking tray. 
9.  Bake for 20–25 minutes, until puffed and golden. 
10.  Turn off the oven and leave the puffs inside for 5 minutes with the door slightly open. 
11.  Remove and cool completely. 

Make the Pastry Cream

1.  Heat the milk in a saucepan until steaming. 
2.  Whisk the egg yolks, sugar, and cornstarch until smooth. 
3.  Slowly whisk the hot milk into the egg mixture. 
4.  Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thick and creamy. 
5.  Stir in the vanilla extract. 
6.  Cover and refrigerate until completely chilled. 

Fill the Cream Puffs

1.  Make a small hole in the bottom or side of each cooled puff. 
2.  Transfer the pastry cream to a piping bag. 
3.  Pipe the chilled pastry cream into each cream puff. 
4.  Dust generously with powdered sugar. 
5.  Serve chilled or slightly cool.