- In a pot off the heat, whisk together the sugar, cornstarch and flour. Add the eggs and whisk until smooth. Add the milk and vanilla. Bring to a boil over medium heat, whisking constantly and scraping the sides and bottom of the pot, until thickened. Strain the pastry cream, if needed. Transfer to a bowl and cover with plastic wrap directly on the surface of the cream. Refrigerate for 3 hours or until completely chilled.
- Meanwhile, with the rack in the middle position, preheat the oven to 375°F (190°C). Line a baking sheet with a silicone mat or parchment paper.
- In a pot, bring 2/3 cup (150 ml) of the water to a boil with the butter, sugar and salt. Remove the pot from the heat. Add the flour all at once and stir vigorously with a wooden spoon until the mixture forms into a smooth ball that pulls away from the sides of the pot.
- Return the pot to medium heat and cook, stirring, for 3 minutes to dry out the dough. This step is crucial for a successful choux pastry. A thin film will form on the bottom of the pot once the dough has sufficiently dried out. Remove from the heat and let cool for 1 minute. Transfer to a bowl or into the bowl of a stand mixer.
- Using a wooden spoon or the paddle attachment, beat in 3 eggs, one at a time, mixing between each addition until the mixture is smooth.
- Transfer into a pastry bag fitted with a ¾-inch (2 cm) plain tip. On the baking sheet, form cream puffs using about 3 tbsp (45 ml) of the mixture for each one, evenly spacing them out.
- In a bowl, whisks the remaining egg with the remaining water. Brush the cream puffs with the egg wash.
- Bake for 25 minutes. Reduce the oven temperature to 325°F (165°C). Bake for another 20 minutes or until the cream puffs look dry and golden. Turn off the oven and let the cream puffs dry out for 30 minutes, keeping the oven door slightly ajar with a wooden spoon. Remove from the oven and let cool completely on the baking sheet.
- In a bowl, whisk the cream, sugar and vanilla with an electric mixer until firm peaks form. Transfer to a pastry bag fitted with a large star tip.
- Cut off the top of each cream puff and fill with the pastry cream (see note). Garnish with banana slices and a few dollops of whipped cream. Close the cream puffs with their tops. Drizzle with the caramel.
It may look like you have too much pastry cream, but there is enough room inside the cream puffs to be quite generous. You can gently tap the bottom of the cream puff on a work surface to help distribute the pastry cream.