Classic Saint-Honoré Tart with Crème Chiboust

Prepare the Puff Pastry Base

1. Preheat oven to 200°C (390°F). Roll out store-bought puff pastry to a 25 cm (10-inch) circle or square. Prick all over with a fork.
2. Bake for 15-20 minutes, or until golden brown and puffed. Remove from oven and let cool completely on a wire rack.

Make the Choux Buns

1. Reduce oven temperature to 180°C (350°F). In a saucepan, bring water, butter, salt, and sugar to a boil.
2. Remove from heat, add flour all at once, and stir vigorously until a ball of dough forms. Return to low heat and cook, stirring, for 1 minute to dry out the dough.
3. Transfer the dough to a bowl and gradually beat in the eggs, one at a time, until the dough is smooth and glossy (it should hold a 'v' shape when lifted with a spoon). You may not need all of the egg.
4. Pipe small choux buns (about 2-3 cm or 1 inch diameter) onto a parchment-lined baking sheet. Bake for 25-30 minutes, or until golden brown and puffed. Let cool.

Prepare the Crème Chiboust

1. Soften gelatin sheets in cold water for 5 minutes (or prepare powdered gelatin as per package instructions).
2. In a saucepan, heat milk with vanilla bean (if using) until simmering. Whisk egg yolks, half of the sugar, and cornstarch until pale.
3. Remove vanilla bean from milk, then slowly pour hot milk into the egg mixture, whisking constantly. Return mixture to the saucepan and cook over medium heat, stirring constantly, until thickened.
4. Remove from heat, stir in softened gelatin until dissolved. Transfer to a bowl, cover with plastic wrap directly on the surface, and let cool slightly.
5. In a separate bowl, whisk egg whites until soft peaks form, then gradually add the remaining sugar and whisk until stiff, glossy peaks form (this is a meringue).
6. Gently fold the cooled pastry cream into the meringue until just combined. Fill the cooled choux buns with crème chiboust using a piping bag.

Assemble the Tart

1. Prepare the caramel: In a heavy-bottomed saucepan, combine sugar and water. Heat over medium-high heat without stirring, gently swirling the pan occasionally, until it turns an amber color.
2. Dip the top of each filled choux bun into the warm caramel, then carefully arrange them around the edge of the puff pastry base, forming a crown. Dip the bottom of each choux bun into caramel as well, if needed, to adhere to the base.
3. Pour the remaining crème chiboust into the center of the tart base and smooth the top. Allow the caramel and crème chiboust to set before serving.
4. Optionally, drizzle some remaining caramel over the top of the tart for decoration.