Prepare the Choux Pastry: In a saucepan, bring water, milk, salt, sugar, and butter to a boil. Stir in the flour all at once and cook until the dough pulls away from the sides. Let cool slightly.
Incorporate the Eggs: Add eggs one at a time, mixing thoroughly after each addition until the dough is smooth and glossy.
Bake the Pastry Shells: Preheat the oven to 200°C (392°F). Pipe or spoon the dough onto a lined baking sheet. Bake for 20-25 minutes until golden and puffed. Let cool completely.
Prepare the Pastry Cream: In a saucepan, whisk together sugar, cornstarch, and milk. Cook over medium heat, stirring constantly until thickened. Remove from heat and stir in vanilla extract. Let cool.
Fill the Cream Puffs: Slice the pastry shells open and fill them with the cooled pastry cream.
Serve & Enjoy: Dust with powdered sugar or drizzle with chocolate for an extra indulgent touch.