Step 1: Make the Choux Pastry Shells

1. Preheat oven to 375°F (190°C).
2. In a saucepan, bring water, butter, and salt to a boil over medium heat.
3. Reduce heat to low, add flour all at once, and stir vigorously with a wooden spoon until a dough forms and pulls away from the pan sides.
4. Remove from heat and let cool for 3–5 minutes.
5. Beat in eggs one at a time until the dough is smooth and glossy.
6. Pipe or spoon dough onto a baking sheet lined with parchment paper into small mounds.
7. Bake for 25–30 minutes or until puffed and golden brown.
8. Cool completely before filling.

Step 2: Make the Custard Filling

1. In a bowl, whisk egg yolks, sugar, and cornstarch until smooth.
2. In a saucepan, heat milk over medium heat until warm but not boiling.
3. Gradually pour milk into the egg yolk mixture while whisking constantly.
4. Return the mixture to the saucepan and cook over low heat, stirring constantly, until it thickens into custard.
5. Remove from heat, stir in vanilla extract, and let it cool.
6. Optional: Fold in whipped heavy cream for a lighter texture.
7. Chill in the refrigerator for at least 30 minutes.

Step 3: Assemble

1. Slice cream puff shells in half or make a small hole in the bottom.
2. Fill a piping bag with chilled custard.
3. Pipe custard into each shell generously.
4. Dust with powdered sugar if desired.
5. Serve chilled for best texture and taste.