Chocolate Royal Cake (also called Trianon) is a classic French entremet made from a hazelnut dacquoise, a praline crunch, a silky dark chocolate mousse, and a glossy cocoa mirror glaze. The layers combine crisp, tender and creamy textures for an elegant showstopping dessert.

General tips:

• Plan ahead: bring ingredients to room temperature and measure them before starting to keep the process smooth.
• Perfectly fluffy dacquoise: whip the egg whites to stiff but not overly firm peaks and sift the dry ingredients for a smooth batter.
• Crispy praline crunch: use fresh crispy wafer cookies (feuilletine) for best crunch; crushed cornflakes can be a substitute.
• Light and creamy mousse: melt chocolate gently over a double boiler and fold whipped cream carefully to keep the mousse airy.
• Glossy mirror glaze: be patient — cool the glaze to about 90–95°F (32–35°C) before pouring to get a shiny surface.
• Organization: assemble in stages; components can be prepared in advance. Freeze the assembled cake before glazing.
• Allow time to defrost: plan for 4–6 hours defrosting in the refrigerator, then 15 minutes at room temperature before serving.

Storage:

• Refrigerate in an airtight container or tightly wrapped for up to 48 hours.
• Freeze the assembled cake without the glaze (wrapped securely) for up to 1 month.

Variations: white chocolate version, coffee-chocolate, hazelnut-caramel, berry layer, tropical or pistachio variations; swap feuilletine for speculoos for a spiced crunch.

Method:

1. Hazelnut Dacquoise
   • Preheat your oven to 350°F (180°C). Line a baking sheet with parchment paper.
   • In a mixing bowl, beat 3 egg whites until stiff peaks form, adding the sugar gradually in three parts.
   • Sift together the hazelnut flour and powdered sugar, then gently fold them into the egg whites using a spatula, making upward motions to preserve the airy texture.
   • Pipe the batter onto the parchment paper using a piping bag or spread it into an 18 cm (7-inch) circle using a tart ring.
   • Bake for 12-15 minutes, until lightly golden. Let the dacquoise cool completely before handling it to prevent breaking.
2. Praline Crunch
   • Crumble the crispy wafer cookies in a bowl.
   • Melt the milk chocolate in a double boiler or microwave.
   • Add the praline paste and melted chocolate to the crumbled cookies and mix until combined.
   • Spread the mixture onto a baking sheet to form an 18 cm (7-inch) circle or directly onto the cooled dacquoise.
   • Place it in the refrigerator to set while preparing the mousse.
3. Chocolate Mousse
   • Chop the baking chocolate into small pieces and place it in a large bowl (or melt it in a double boiler if preferred).
   • Bring the whole milk to a boil in a saucepan. In the meantime, whisk the egg yolks and sugar in a separate bowl until slightly frothy.
   • Pour the hot milk over the yolk and sugar mixture, whisking constantly.
   • Return the mixture to the saucepan and cook over low heat, stirring continuously, until it thickens slightly (about 181°F/83°C, or until it coats the back of a spoon).
   • Pour the warm custard over the chopped chocolate and stir with a spatula until the chocolate is fully melted and the ganache is smooth.
   • Whip the cold heavy cream into firm peaks using an electric mixer.
   • Gently fold a small amount of whipped cream into the ganache to loosen it, then carefully fold in the remaining whipped cream with a spatula until the mousse is smooth and creamy.
4. Assembly
   • Place a 20 cm (8 inch) pastry ring on a tray and seal the bottom with plastic wrap to create a base.
   • Line the inside of the ring with acetate if possible.
   • Spread a small amount of chocolate mousse at the bottom of the ring and smooth it out to fill any gaps. Add the rest of the mousse to fill the ring.
   • Place the praline crunch layer and the dacquoise on top, pressing gently to push them slightly into the mousse.
   • Cover and freeze for at least 4-6 hours, preferably overnight.
5. Mirror Glaze
   • Rehydrate the gelatin sheets in cold water for 5-10 minutes.
   • Bring the sugar and water to a boil in a saucepan.
   • Sift the cocoa powder into a bowl or pitcher. Pour the hot sugar syrup over it, stirring until smooth.
   • Add the drained gelatin sheets and stir until fully dissolved.
   • Incorporate the lightly heated heavy cream and blend with an immersion blender. Strain the glaze through a fine mesh sieve, then blend again, keeping the blender head submerged to avoid air bubbles.
6. Whipped Ganache
   • Heat ⅓ (60 g) of the heavy cream until it simmers.
   • Pour it over the chopped chocolate and stir gently until the ganache is smooth.
   • Add the remaining cold heavy cream to the warm ganache and mix well.
   • Chill in the refrigerator for at least 4 hours or overnight. On the day of serving, whip the chilled ganache with an electric mixer until it reaches a firm and airy texture.
7. Decoration
   • Remove the cake from the freezer and carefully release it from the pastry ring (using a kitchen torch on the sides can help).
   • Place the cake on a wire rack or flat surface like an inverted pan or large glass, with a tray underneath to catch the excess glaze.
   • When the mirror glaze cools to 90-95°F (32-35°C), pour it evenly over the frozen cake to fully coat it.
   • Quickly smooth the top and sides with a spatula to remove excess glaze.
   • Transfer the Chocolate Royal to a serving plate or cake stand.
   • Decorate with whipped ganache, chocolate shavings, or any toppings of your choice.
   • Allow the cake to defrost in the refrigerator for at least 3-4 hours before serving.