Religieuses are classic French choux pastries made from two cream-filled puffs stacked and glazed to resemble a figure in a habit — which is how they got their name, meaning "nuns." Each pastry is piped with pastry cream, coated in fondant icing, and finished with a ring of buttercream. Plan for about 2 hours from start to finish.
Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.
In a saucepan over medium heat, combine water, butter, sugar, and salt. Stir until butter melts completely.
Add the flour all at once and stir vigorously with a wooden spoon until the mixture forms a ball and pulls away from the sides of the pan.
Transfer the dough to a mixing bowl. Let it cool slightly. Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.
Transfer the dough into a piping bag fitted with a round nozzle. Pipe small rounds for the top and larger rounds for the base onto the baking sheet. Bake for 25-30 minutes or until puffed and golden. Cool on wire racks.
For the Pastry Cream:
In a saucepan, combine milk and half the sugar. Bring to a simmer.
In a bowl, whisk together the remaining sugar, cornstarch, flour, and egg yolks until smooth.
Gradually whisk the hot milk into the egg mixture. Return to saucepan and cook over medium heat, stirring constantly until thickened.
Remove from heat, stir in vanilla and butter until smooth. Cool before using.
For the Chocolate Ganache:
Heat the cream in a saucepan until it just begins to simmer.
Pour over the chopped chocolate. Let sit for a minute then stir until smooth.
Assembly:
Fill a piping bag with cooled pastry cream, pierce each choux and fill.
Dip the tops of the choux in chocolate ganache. Stack small choux on top of larger ones.
Optional: Decorate further with piped frosting or whipped cream if desired.
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Notes
For a richer flavor, use a high-quality vanilla bean instead of extract by infusing it with the milk.
For a lighter cream, fold in some whipped cream gently before filling.