Hazelnut Dacquoise

1. Preheat your oven to 350°F (180°C). Line a baking sheet with parchment paper.
2. In a mixing bowl, beat 3 egg whites until stiff peaks form, adding the sugar gradually in three parts.
3. 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.
4. 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.
5. Bake for 12-15 minutes, until lightly golden. Let the dacquoise cool completely before handling it to prevent breaking.

Praline Crunch

1. Crumble the crispy wafer cookies in a bowl.
2. Melt the milk chocolate in a double boiler or microwave.
3. Add the praline paste and melted chocolate to the crumbled cookies and mix until combined.
4. Spread the mixture onto a baking sheet to form an 18 cm (7-inch) circle or directly onto the cooled dacquoise.
5. Place it in the refrigerator to set while preparing the mousse.

Chocolate Mousse

1. Chop the baking chocolate into small pieces and place it in a large bowl (or melt it in a double boiler if preferred).
2. 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.
3. Pour the hot milk over the yolk and sugar mixture, whisking constantly.
4. 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).
5. Pour the warm custard over the chopped chocolate and stir with a spatula until the chocolate is fully melted and the ganache is smooth.
6. Whip the cold heavy cream into firm peaks using an electric mixer.
7. 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.

Assembly

1. Place a 20 cm (8 inch) pastry ring on a tray and seal the bottom with plastic wrap to create a base.
2. Line the inside of the ring with acetate if possible.
3. 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.
4. Place the praline crunch layer and the dacquoise on top, pressing gently to push them slightly into the mousse.
5. Cover and freeze for at least 4-6 hours, preferably overnight.

Mirror Glaze

1. Rehydrate the gelatin sheets in cold water for 5-10 minutes.
2. Bring the sugar and water to a boil in a saucepan.
3. Sift the cocoa powder into a bowl or pitcher. Pour the hot sugar syrup over it, stirring until smooth.
4. Add the drained gelatin sheets and stir until fully dissolved.
5. 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.

Whipped Ganache

1. Heat 1/3 (60 g) of the heavy cream until it simmers.
2. Pour it over the chopped chocolate and stir gently until the ganache is smooth.
3. Add the remaining cold heavy cream to the warm ganache and mix well.
4. 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.

Decoration

1. Remove the cake from the freezer and carefully release it from the pastry ring (using a kitchen torch on the sides can help).
2. 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.
3. When the mirror glaze cools to 90-95°F (32-35°C), pour it evenly over the frozen cake to fully coat it.
4. Quickly smooth the top and sides with a spatula to remove excess glaze.
5. Transfer the Chocolate Royal to a serving plate or cake stand.
6. Decorate with whipped ganache, chocolate shavings, or any toppings of your choice.
7. Allow the cake to defrost in the refrigerator for at least 3-4 hours before serving.