- Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper or a silicone mat.
- In a saucepan, bring the water, butter and salt to a boil. Remove from the heat. Add the flour all at once and stir vigorously with a wooden spoon until the dough forms a smooth ball that comes off the sides of the pan.
- Return the pan over low heat and cook while stirring for 1 minute. Remove from the heat and let cool for 1 minute.
- In a stand mixer fitted with the paddle attachment, in a food processor or with a wooden spoon, add the eggs, one at a time, stirring thoroughly after each addition, until smooth.
- With a pastry bag fitted with a ½-inch (1 cm) plain tip and filled with choux pastry dough, shape approximately 27 choux (balls) about the size of a loonie on the baking sheet.
- Bake for about 25 minutes or until golden brown. With a small knife, slit the choux on the side to allow steam to escape. Return them to the still-warm oven, turned off, for about 10 minutes to dry them slightly. Let cool on a wire rack.
- In a saucepan off the heat, combine the sugar, flour and cornstarch. Add the eggs and mix thoroughly with a whisk. Stir in the milk and vanilla. Cook over medium-high heat, stirring continuously while scraping the sides of the pan until the mixture thickens. Remove from the heat.
- Strain the custard through a sieve into a bowl, if needed. Cover with plastic wrap directly on the surface of the custard. Let cool and refrigerate for 2 hours or until completely chilled. When ready to use the custard, stir with a spatula to soften it.
- In another saucepan, off the heat, combine the sugar, cocoa powder and cornstarch. Add the cream and bring to a boil over medium-high heat, stirring with a whisk. Let simmer for 10 seconds. Pour into a bowl. Cover with plastic wrap directly on the surface of the sauce. Let cool or refrigerate until ready to serve. The fudge sauce will keep for about 1 week.
- In a bowl, whip the cream, sugar and vanilla with an electric mixer until stiff peaks form.
- At the bottom of a 12-cup (3 litre) glass serving bowl, spread ½ cup (125 ml) of the whipped cream and a third of the choux. Add half of the vanilla custard, half the fudge sauce and half the whipped cream. Repeat the sequence a second time, finishing with ¼ cup (60 ml) of fudge sauce and the remaining choux. Refrigerate for 12 hours before serving.