Opera Cake: A French Layer Cake That Tests Even Expert Bakers

Anyone with a sweet tooth probably knows Opera cake. It is delicious and intensely rich, and it is also a cake that challenges even expert bakers. Let's see why.

Opera cake is a French cake. The original is made of almond sponge, called joconde in French, soaked with coffee syrup, spread with coffee buttercream and chocolate ganache, and finished with a chocolate glaze on top.

Today, Opera cake has been adapted into many more flavours, but its signature remains its tall stack of layers, said to be like an opera made up of several acts. Let's look at the ingredients and method and see just how challenging it is.

Ingredients

Joconde (almond sponge cake)

1. 3 large egg whites
2. 2 tbsp sugar
3. 1 cup ground almonds
4. 1 cup icing sugar, sifted
5. 3 whole eggs
6. 1/4 cup all-purpose flour
7. 2 tbsp unsalted butter, melted (melt it when you start whipping the egg whites and leave it in the microwave so it doesn't set again)

Coffee syrup

1. 1 1/2 tsp instant coffee powder
2. 1/4 cup water + 1 tbsp warm water (for dissolving the coffee)
3. 1/4 cup sugar
4. 1–2 tbsp Irish cream liqueur or brandy (optional)

Coffee buttercream

1. 2 tsp instant coffee powder
2. 1/4 cup water + 1 tbsp warm water (for dissolving the coffee)
3. 6 tbsp sugar
4. 2 egg yolks
5. 1 stick (113 g) unsalted butter, softened at room temperature

Chocolate ganache filling

1. 120 g bittersweet chocolate (60% cacao)
2. 120 g whipping cream

Chocolate base

1. 90 g dark chocolate
2. 10 g vegetable oil

Chocolate glaze

1. 100 g dark chocolate
2. 170 g whipping cream
3. 1 tbsp light corn syrup

Method

Joconde (almond sponge cake)

1. Butter a 12.5 x 15.5 inch baking tray, line it with baking paper, then butter the paper as well (we found this recipe needs buttered paper, or the cake sticks and is hard to peel off). Preheat the oven to 400°F (200°C).
2. Whip the egg whites with a hand mixer at medium speed until fine bubbles form. Gradually add the sugar and whip at high speed to stiff, smooth, glossy peaks. Set aside.
3. In another medium bowl, beat the whole eggs, icing sugar and ground almonds until well combined and pale, ideally for no more than 1 minute (we noticed that the longer you beat, the more air bubbles the cake has and the drier it gets). Gradually sift in the flour and fold in with a rubber spatula, taking care not to overmix (you can also use a hand mixer on low speed; it's quicker and works just as well).
4. Fold in the egg whites about one third at a time with a rubber spatula.
5. Pour in the melted butter while folding with the spatula until well combined.
6. Pour the batter into the prepared tray and bake for about 8–9 minutes (depending on your oven). To check, touch the centre of the cake: if it springs back, it's done.
7. Turn the cake out onto a rack, peel off the paper and let it cool completely. Then cut it crosswise into three equal pieces by eye. You don't need to trim the uneven edges yet, but you can trim a little to be safe if you like.

Coffee syrup

1. Dissolve the coffee powder in 1 tbsp warm water and set aside.
2. Boil the remaining water with the sugar until the sugar has dissolved.
3. Remove from the heat, stir in the dissolved coffee and Irish cream, and let cool completely.

Coffee buttercream

1. Dissolve the coffee powder in 1 tbsp warm water and set aside.
2. Put the remaining water and the sugar into a small saucepan over medium heat and stir until the sugar dissolves, then stop stirring and let the syrup boil. Brush down any sugar crystals on the sides of the pan. Boil until the syrup reaches 238°F (just before soft-ball stage). Without a thermometer, judge by eye: the syrup should be slightly thick with small, rapid bubbles.
3. While the syrup boils, beat the egg yolks with a hand mixer at medium speed for about 1 minute.
4. Take the syrup off the heat and pour it in a thin stream into the yolks while beating continuously. Once all the syrup is in, add the dissolved coffee and keep beating until the mixture cools, about 3–4 minutes. Then add the softened butter 1–2 tablespoons at a time, beating well after each addition. Keep beating briefly until you have a smooth, thick cream.

Chocolate ganache filling

1. Heat the cream in the microwave on high until it starts to boil, about 45 seconds to 1 minute.
2. Pour it over the chocolate and leave for 1–2 minutes, then gently whisk from the centre outwards until smooth. Set aside.

Chocolate base

Melt the chocolate over a pan of hot water (water brought just to the boil, steaming, then taken off the heat). Add the vegetable oil and whisk until smooth.

Chocolate glaze

Put the cream and light corn syrup in a heatproof cup and microwave on high for about 1 minute, or until the cream just starts to boil. Pour over the chocolate, leave for 1–2 minutes, then stir from the centre until the glaze is smooth and glossy.

Assembling the cake

1. Divide the cake into three equal pieces as described above. Spread the chocolate base over one side of the first piece and chill for about 15 minutes until the chocolate sets.
2. Turn it over onto baking paper, chocolate side down. Soak the top with coffee syrup, then spread with coffee buttercream and chill for about 15 minutes until the buttercream firms. Spread the chocolate ganache filling over the buttercream and chill for about 15 minutes until the ganache sets. Repeat with the other two pieces of cake: syrup, buttercream and ganache. Finally pour the chocolate glaze over the top and chill overnight, or until well set.
3. Once the chocolate has set, trim the edges, cut the cake into pieces and pipe the word "Opera" on top with the leftover ganache filling. If there's none left, just make a little more, or decorate however you like.

Tips

1. For even layers of cream and ganache, divide them equally: 1/2 cup of buttercream per layer and 1/4 cup of ganache filling per layer. The top layer can be a little under 1/4 cup, which is fine because it will be covered with chocolate glaze.
2. If the ganache filling thickens and becomes hard to spread during assembly, stir it over a pan of hot water for a moment to soften it.