Opera Cake

Preheat the oven to 220°C (200°C fan). Line two 30×40cm rimmed baking trays with parchment and grease lightly. Whisk the ground almonds, icing sugar, and whole eggs together in a stand mixer on high speed for 5 minutes until pale, thick, and ribbon-forming. In a separate clean bowl, whisk the egg whites to soft peaks, then add the caster sugar and whisk to stiff, glossy peaks. Sift the flour over the almond mixture and fold gently, then fold in one-third of the meringue to loosen, followed by the remaining meringue in two additions. Drizzle the melted butter down the side of the bowl and fold until just combined.

Divide the batter evenly between the two prepared trays and spread to a thin, even layer with an offset spatula. Bake for 5–7 minutes until the sponge is golden, springs back when pressed, and pulls away slightly from the edges. Turn each sheet out onto a wire rack, peel off the parchment, and leave to cool completely.

Make the coffee syrup by combining the water and caster sugar in a small saucepan over medium heat, stirring until the sugar dissolves, then bringing to a simmer for 2 minutes. Remove from the heat, stir in the espresso powder, and leave to cool completely.

Make the ganache by heating the double cream in a small saucepan over medium heat until it just begins to steam and tiny bubbles appear around the edge — do not boil. Pour over the chopped chocolate in a heatproof bowl and leave undisturbed for 2 minutes, then stir from the centre outward until smooth. Add the butter and stir until glossy. Set aside at room temperature to firm to a spreadable consistency, about 30 minutes.

Make the French buttercream by beating the egg yolks in a stand mixer on high speed until pale and thick, about 3 minutes. Meanwhile, combine the caster sugar and water in a small saucepan over medium-high heat and cook, without stirring, until the syrup reaches 118°C on a sugar thermometer. With the mixer running on medium, pour the hot syrup in a slow, steady stream down the side of the bowl onto the yolks, avoiding the whisk. Increase speed to high and whisk until the mixture is thick, pale, and the bowl feels cool to the touch, about 8 minutes.

With the mixer on medium, add the softened butter a few cubes at a time, beating well after each addition until the buttercream is smooth, silky, and holds its shape. Beat in the cooled espresso mixture. If the buttercream looks curdled, continue beating — it will come together.

Cut each cooled joconde sheet into equal rectangles to fit your serving frame or line a 20×15cm deep-sided tray. You need three sponge layers in total — cut one sheet into two pieces if necessary. Place the first sponge layer on a parchment-lined tray and brush generously with coffee syrup until thoroughly soaked.

Spread an even, thin layer of chocolate ganache over the first soaked sponge using an offset spatula, taking it right to the edges. Refrigerate for 10 minutes until just set.

Place the second sponge layer on top and brush thoroughly with coffee syrup.

Spread an even layer of coffee buttercream over the second soaked sponge, smoothing it perfectly flat. Refrigerate for 10 minutes until firm.

Place the third sponge layer on top and brush thoroughly with coffee syrup.

Spread a final, thin, even layer of coffee buttercream over the third sponge. Refrigerate for at least 1 hour until completely firm.

Make the chocolate glaze by heating the double cream in a small saucepan over medium heat until steaming, then pouring over the chopped chocolate in a heatproof bowl. Leave for 2 minutes, stir until smooth, then add the butter and oil and stir until glossy and fluid. Leave to cool until the glaze reaches 32°C — it should coat the back of a spoon thickly without setting immediately.

Pour the glaze over the chilled gâteau and tilt the tray gently to spread it to all four edges in a perfectly level, mirror-smooth layer. Refrigerate uncovered for at least 2 hours until the glaze is completely set.

To serve, trim 5mm from each edge with a long, sharp knife dipped in hot water and wiped dry between each cut to reveal the clean, defined layers. Slice into four equal portions with the same technique.