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Opéra-style Chocolate Cake

The classic opéra gateau is a multi-layered sponge cake sandwiched together with chocolate ganache and buttercream and topped with fruit. here is my take on it, which uses brownie-style chocolate sponge, three types of chocolate mousse and chocolate glazing. It should be prepared a day before required, because it’s quite complicated and must be frozen overnight.

Serves 12–16

Ingredients

  • 90g (3 1⁄2oz) dark (semisweet) chocolate (at least 70 per cent cocoa solids)
  • 135g (1 stick plus 11⁄2 tbsp) butter, softened
  • 135g (2⁄3 cup) caster (superfine) sugar
  • 2 eggs
    65g (1⁄2 cup) plain (all-purpose) flour
  •  
  • For the dark chocolate mousse
  • 125g (4 1⁄2oz) dark chocolate(at least 70 per cent cocoa solids), chopped
  • 1 egg, separated
    250ml (1 cup) double (heavy) cream, lightly whipped to soft peaks
  •  
  • For the milk chocolate mousse
  • 125g (4 1⁄2oz) milk chocolate (33 per cent cocoa solids), chopped
  • 1 egg, separated
    200ml (3⁄4 cup plus 2 tbsp) double cream, lightly whipped
  •  
  • For the white chocolate mousse
  • 125g (4 1⁄2oz) white chocolate (28 per cent cocoa solids), chopped
  • 1 egg, separated
    200ml (3⁄4 cup plus 2 tbsp) double cream, lightly whipped
  •  
  • For the chocolate glaze
  • 90g (31⁄2oz) dark chocolate (at least 70 per cent cocoa solids), finely chopped
  • 150ml (2⁄3 cup) double cream
  • 30ml (2 tbsp) water
    40g (3 tbsp) runny honey
  • 25g (2 tbsp) butter, cubed

 

Method

  1. Preheat the oven to 180°C/350°F/gas mark 4. Line three 22 x 22cm (9 x 9 inch) baking sheets with greaseproof (wax) paper.
  2. Sponge
    1. Melt the chocolate in a heatproof bowl set over a saucepan of simmering water, making sure the bottom of the bowl does not touch the water.
    2. Put the butter in another bowl and beat until soft.
    3. Place the sugar and eggs in a third bowl and beat until pale and fluffy.
    4. Remove the chocolate from the heat and fold in the soft butter. Combine with the egg mixture, then sift in the flour. Mix with spatula until no pockets of flour are left.
    5. Divide the mixture equally among the prepared baking sheets and spread into an even layer 5mm (1⁄4 inch) thick. (a) Bake for 6–8 minutes. Transfer to a wire rack to cool. Dark chocolate mousse
    6. Melt the chocolate in a heatproof bowl set over a saucepan of simmering water, making sure the bottom of the bowl does not touch the water. Leave to cool slightly, until about 45–50°C/113–122°F.
    7. Lightly beat the egg yolk, then add to the melted chocolate and stir well with a spatula. Fold in one- third of the whipped cream, then whisk in the remainder. It will soften the mixture and loosen its consistency.
    8. Put the egg white into a clean bowl and whisk until stiff. Gently fold into the chocolate cream mixture. Set aside.
  3. Milk chocolate mousse
    1. Make in the same way as the dark chocolate mousse.
  4. White chocolate mousse
    1. Make in the same way as the dark chocolate mousse.
  5. To build the cake
    1. Line a deep baking tin 22 x 22cm (9 x 9 inches) with three layers of clingfilm (plastic wrap), allowing it to generously overhang the edges. Build the layers of the cake as follows: sponge, dark chocolate mousse, sponge, milk chocolate mousse, sponge, white chocolate mousse. Cover with the overhanging clingfilm and freeze overnight.
  6. Chocolate glaze
    1. Melt the chocolate in a heatproof bowl set over a saucepan of simmering water, making sure the bottom of the bowl does not touch the water.
    2. Put the cream, water and honey in a small saucepan and bring to the boil.
    3. Pour one-third of the boiled cream mixture on to the melted chocolate and mix with a spatula until shiny. Add another third, combine again, then add the final third. Leave to cool to 35–40°C/95–104°F, then add the butter.
    4. Place the frozen cake on a wire rack over a tray (to catch any drips) and pour the glaze over it. Spread it out smoothly with a rubber spatula or palette knife, then place in the refrigerator for 4–6 hours to set.
    5. Before serving, trim the cake edges evenly using a knife dipped in warm water. Use the same technique to cut the cake into slices