1. In a saucepan, combine butter, water, and salt. Bring to a boil.

2. Stir in flour all at once and stir vigorously until the dough pulls away from the sides of the pan. Let it cool for 5 minutes.

3. Beat in the eggs one at a time, mixing until the dough is smooth and glossy.

4. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.

5. Pipe the choux dough into 1.5-inch mounds on the baking sheet.

6. Smooth any peaks with a wet finger.

7. Bake for 25–30 minutes until golden brown and firm. Cool completely.

8. To make the pastry cream, heat milk and nutmeg in a saucepan until steaming.

9. In a bowl, whisk egg yolks, sugar, and cornstarch.

10. Gradually whisk in the hot milk, then return mixture to saucepan.

11. Cook over medium heat, whisking constantly, until thickened.

12. Remove from heat and stir in butter, vanilla, and rum extract if using.

13. Transfer to a bowl, cover with plastic wrap touching the surface, and chill until set.

14. Slice each choux puff or poke a hole in the bottom and pipe in the pastry cream.

15. Dust tops with powdered sugar before serving.