Instructions

1. Preheat oven to 400 F (200 C). Lightly grease sides of 9-in (23 cm) springform pan and line bottom with parchment paper. Set aside.
2. On clean surface, roll out puff pastry to roughly 10-in (25 cm) square and place on a parchment-lined baking sheet. Using a fork, poke holes across surface of pastry, then bake for 15 minutes. Remove from oven and cool to room temperature.
3. Leaving pastry on parchment-lined baking sheet, place base of springform pan over pastry and, using a sharp knife, cut around edges to make a 9-in (23 cm) circle. Discard remaining pastry.
4. Preheat oven to 375 F (190 C).
5. Fill a large piping bag fitted with a ½-in (1.25 cm) round tip (or similar) with prepared Choux Pastry Dough. Pipe a circle around edge of puff pastry base about ½-in (1.25 cm) from edge. Pipe a 1½-in (3.75 cm) round in centre. Then pipe a circle between outer and inner piped circles.
6. On another parchment-lined baking sheet, pipe a tiny bit of pastry under parchment paper at all 4 corners. Gently press down corners to help paper stick to baking sheet.
7. Pipe 1½-in (3.75 cm) round mounds, about 2-in (5 cm) apart. Gently press pointy peaks with moistened finger to smooth tops.
8. In a small bowl, lightly whisk together egg and water. Gently brush egg wash over tops of all prepared choux pastry, including the circles on puff pastry base. Bake until golden brown, about 25 to 30 minutes. Do not open oven while baking. Once baked, remove from oven and allow to cool completely.
9. Meanwhile, prepare Chocolate Crème Chiboust (recipe below). Gently, puncture bottom of each round choux pastry with nozzle and fill with Chocolate Crème Chiboust until you feel the edge of puff gently push back in your hand. Place on lined baking sheet and refrigerate for at least 1 hour.
10. Place puff pastry circle with baked choux circles in prepared springform pan. Gently puncture small holes in baked choux circles on puff pastry circle with nozzle and fill with Chocolate Crème Chiboust. Pipe any remaining filling into gaps between circles and smooth surface with an offset spatula. Refrigerate for at least 1 hour.
11. Place chopped chocolate in medium, heatproof, non-reactive bowl. In a small saucepan over medium heat, bring ¾ cup (175 ml) whipping cream to a gentle simmer, not boil. Pour over chopped chocolate and let it rest for 1 minute to melt chocolate. Then whisk until smooth and glossy.
12. Dip each cream puff into chocolate ganache and carefully place on baking sheet. Once you have enough cream puffs to line inner circumference of springform pan, pipe a tiny amount of ganache at base of each cream puff and place on top of choux circle along outer edge. Refrigerate.
13. In large bowl, whip together mix 2 cups (500 ml) whipping cream, cocoa powder, sugar and vanilla extract until soft peaks form. Transfer to large piping bag fitted with large St. Honoré piping tip. Remove outer ring of springform pan and pipe as desired on top of cake. Garnish with gold leaf, if using. Refrigerate until ready to serve.
14. FOR CHOUX PASTRY DOUGH, In a medium saucepan over medium heat, melt together water, butter, sugar and salt and bring to a boil.
15. Remove from heat and add flour. Using a wooden spoon, mix until fully incorporated. Return to heat and cook mixture for 2 to 3 minutes, until a thin layer sticks to bottom of pan while stirring and mixture comes together as a dough.
16. Transfer dough to a large bowl and allow to cool slightly.
17. Using a wooden or silicon spoon, add 1 egg at a time and mix dough until each egg is fully incorporated. Dough should be soft and able to hold stiff peaks when lifted. Use as needed.
18. FOR CHOCOLATE CRÈME CHIBOUST, In small heatproof bowl, sprinkle gelatin in water and set aside to bloom.
19. In another medium bowl, whisk together egg yolks, cornstarch, 2 tbsp (30 ml) sugar and salt until fully incorporated and no lumps remain.
20. Place chopped chocolate in a small heatproof bowl over a small saucepan of gently boiling water, making sure bottom of bowl of chocolate does not touch boiling water. Stir constantly until chocolate is melted. Remove from heat and set aside.
21. In medium saucepan, over medium heat, bring milk and instant coffee powder to boil. Remove from heat and slowly transfer ⅓ cup (75 ml) to egg mixture, whisking constantly making sure not to cook eggs. Add back to saucepan with remaining milk and stir vigorously. Return to heat and continue cooking until mixture thickens to consistency of thick sauce only, not paste.
22. Remove from heat. Add melted chocolate and bloomed gelatin. Mix well until smooth. Cover with plastic wrap and set aside to cool at room temperature.
23. In a standing mixer, whisk egg whites until frothy over medium speed.
24. In a small saucepan, boil 1 cup (250 ml) sugar and ⅓ cup (75 ml) water until mixture reaches 248 F (120 C) on a candy thermometer.
25. With stand mixer on medium speed, slowly pour melted sugar syrup into egg whites. Turn off mixer and scrape down sides of bowl to ensure sugar is well integrated into mixture. Turn mixer back on and whisk meringue on high speed until stiff peaks form.
26. Using a hand mixer, whisk chocolate crème until smooth and fluffy. Fold in ⅓ of whipped meringue into chocolate crème until no white streaks remain. Add remaining egg whites and fold in until fully incorporated. Transfer to a large piping bag fitted with a narrow choux pastry filling injector nozzle and use as needed.