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Royal Chocolate Cake (Trianon / Gâteau Royal)

Sliced Royal chocolate cake on a golden cake board with crepes Gravottes on background.
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Royal chocolate cake (Trianon or gâteau Royal) is a French dark chocolate mousse cake made of nut dacquoise, a crispy layer of crepes Gavottes, and dark chocolate mousse. Follow this recipe to make Royal chocolate cake at home.

Ingredients

Scale

For the dacquoise:

  • 3 1/2 tablespoons (55 g) egg whites (see note #1)
  • 2 1/2 tablespoons (35 g) granulated sugar
  • 1/2 cup + 1 teaspoon (65 g) icing sugar
  • 1/3 cup (30 g) almond flour
  • 2 tablespoons (15 g) hazelnut flour/meal

For the crunchy praline feuillantine:

  • 1.7 oz (50 g) crepes Gravottes
  • 1.7 oz (50 g) milk chocolate
  • 1.7 oz (50 g) hazelnut spread Nutella
  • 1.7 oz (50 g) Hazelnut Praline Paste

For the chocolate mousse:

  • 2 cups + 3 tablespoons (500 ml) whipping cream
  • 5 tablespoons (75 g) whole milk
  • 7 oz (200 g) dark chocolate 

For the cocoa mirror glaze:

  • 2/3 cup + 4 1/2 tablespoons (210 g) granulated sugar
  • 5 tablespoons (75 g) water
  • 9 1/2 tablespoons (70 g) cocoa powder, unsweetened
  • 1/2 cup + 2 tablespoons (145 ml) whipping cream
  • 3 1/3 gelatin sheets (8 g powdered gelatin - see note #2)

*Don't you have the correct baking pan on hand right now? Try this simple Cake Pan Converter!

** If needed, please refer to Baking Conversion Charts.

Instructions

  1. To make the dacquoise, preheat the oven to 335°F (170°C). Using a flour sifter, sift powdered (icing) sugar, almond, and hazelnut flour. In a separate bowl, whisk the egg whites, then gradually add granulated sugar until slightly firm. Once the meringue is ready, add the icing sugar/flour mixture and gently mix with a spatula.
  2. Transfer the preparation to a pastry bag with Ateco plain pastry tip 809. Adjust a mousse cake mold to 7 inches/18 cm in diameter. Pipe a spiral inside the mold placed on a baking sheet with parchment paper, or simply use a spoon. Bake for 20 to 25 minutes. Let it cool in a frame. 
  3. To make the crunchy praline feuillantine, roughly crush the crepes Gavottes with your hands or a rolling pin. Melt milk chocolate in a bain-marie (water bath). Place hazelnut praline, Nutella, and crepe chips in a bowl and mix. Add melted chocolate and mix again.
  4. Use a knife to loosen the dacquoise from the mold, but keep it in the mold. Pour the crunchy mixture over the dacquoise, and spread it into a thin layer. Then remove the mold and freeze the dacquoise for about 10 to 15 minutes. 
  5. To make the chocolate mousse, whip the cold whipping cream in a bowl until stiff peaks form, then refrigerate. Melt dark chocolate broken into small pieces in a bain-marie/water bath. Bring milk to a boil, pour it over the melted chocolate, and mix with a rubber spatula until smooth. When the chocolate mixture is lukewarm, add it to the whipped cream and mix with a spatula as fast as possible. Transfer the mousse to a pastry bag with a plain tip.
  6. To assemble the cake, seal one side of the 8-inch/20 cm cake ring with a plastic film and place it on a wooden board or a baking sheet. Insert an acetate collar inside the ring. Poach the chocolate mousse in the mold, raising it up the sides of the ring with a rubber spatula. Take the dacquoise disk from the freezer, turn it over, and place it over the mousse (dacquoise side up). Slightly press the disk and remove the excess mousse with a bent spatula. Cover with a plastic film and freeze for at least 5 hours.
  7. To make the cocoa mirror glaze, soak gelatin sheets in cold water for 10 minutes. Heat whipping cream over low heat and set aside. Pour water and sugar into a saucepan and bring to a boil. Once the sugar syrup starts boiling actively, pour it over the sifted cocoa powder and gently mix, avoiding air bubbles. Add the drained gelatin and mix it with a hand blender. Then pout hot whipping cream and mix again. Pass the mixture through a fine-mesh sieve and mix with a hand blender. Let the glaze cool down to 86°F/30°C.
  8. To glaze the cake, remove the dessert from the freezer. Place the cake on a wire rack or a plate, which is itself placed on a baking sheet to collect the excess glaze. Remove the plastic film, mold (heat the sides of the ring with a blow torch), and the acetate collar. Pour the glaze over the cake, then remove the excess with a bent spatula, passing it over the top once. Transfer the dessert to a cake board using two metal spatulas. Place the cake in the fridge to thaw for 3 to 4 hours.

Notes

  1. 55 g egg whites approximately equal 1 1/2 raw egg whites from extra-large chicken eggs.
  2. To substitute sheet gelatin, use 8 g of powdered gelatin and 1/4 cup (60ml) of cold water.
  3. Do not overwhisk the egg whites when making the dacquoise. They have to be slightly firm to incorporate the nut flour.
  4. Spread the chocolate mousse well inside the mold, using a rubber spatula to avoid trapping air in the cake.
  5. Once the cocoa mirror glaze is applied, use a bent metal spatula to remove excess in a single pass over the top of the cake, avoiding marks.
  6. Store the decorated cake in the fridge for 2 to 3 days.
  7. Take the dessert out of the fridge for about 20 minutes before tasting it (cold temperatures alter the chocolate's flavor).

Nutrition

Find it online: https://www.bakinglikeachef.com/royal-chocolate-cake-by-christophe-felder/