For the Pastry Cream:

1. Heat milk in a saucepan until steaming, not boiling. Stir in vanilla.

2. In a bowl, whisk sugar, cornstarch, salt, and egg yolks until smooth.

3. Temper the egg mixture by slowly whisking in ½ cup of the hot milk.

4. Return mixture to saucepan and whisk constantly over medium heat until thickened, 2–3 minutes.

5. Remove from heat; whisk in butter and rum (if using).

6. Pour into a bowl, press plastic wrap directly on the surface, and chill for 2–3 hours.

For the Choux Pastry:

1. Preheat oven to 400°F and line a baking sheet with parchment.

2. In a saucepan, heat water, milk, butter, sugar, and salt to a boil.

3. Reduce heat and add flour all at once. Stir vigorously until a ball forms, about 1 minute.

4. Transfer to a mixing bowl. Cool 5 minutes.

5. Beat on low speed 30 seconds, then add eggs one at a time, mixing well after each. Mix 1 minute more until smooth and pipeable.

6. Pipe 1¾-inch mounds onto the sheet. Wet your finger and smooth tips.

7. Bake 22–25 minutes without opening oven.

8. For piped filling: poke a ¼-inch hole in bottom/side of each puff. Return to oven with heat off and door cracked for 30 minutes.

9. For sliced filling: skip poking and leave in oven to dry with heat off.

To Assemble:

1. Whisk chilled pastry cream until smooth.

2. Pipe cream into the hole, or slice and spoon/pile cream into the center.

3. Dust with confectioners’ sugar and serve immediately.