Preheat oven to 200°C (390°F) and line a baking sheet with parchment paper.

Bring water, butter, and salt to a boil in a saucepan, then remove from heat.

Add flour all at once and stir vigorously until dough pulls from pan sides.

Cool slightly, then beat in eggs one at a time until smooth and glossy.

Pipe or spoon dough into a ring shape and bake for 30-35 minutes until puffed and golden. Let cool completely.

Beat cream cheese, powdered sugar, and vanilla until smooth. Fold in whipped cream (and custard if using) until fluffy.

Slice cooled pastry ring horizontally, spread or pipe filling generously inside, then replace top half.

Dust with powdered sugar and chill for at least 1 hour before serving.