Opera cake is traditionally made with an almond sponge, coffee soak, chocolate ganache, and coffee buttercream. In this version we are making one very similar to the classic but using hazelnuts in place of almonds in our sponge layer. The base of the cake is a hardened chocolate shell. This shell provides a little crunch. On top of the chocolate, there are layers of hazelnut sponge, coffee buttercream, and chocolate ganache.

Components of Opera Cake:

Thin, hardened chocolate layer
Hazelnut sponge
Coffee liquor soak
Coffee buttercream
Chocolate ganache

Opera Cake with Hazelnut sponge

Ingredients

Chocolate Ganache:

3 oz chopped dark chocolate
2 tablespoons salted butter 29 g
3/8 cup granulated sugar 75 g
3/8 cup heavy cream 90 ml
1 teaspoons vanilla extract 5 ml
Pinch of salt

Coffee Buttercream:

10 ounces salted butter room temperature
8 ounces granulated sugar
4 ounces egg whites
½ teaspoon salt
¼ cup espresso cooled (or strong brewed coffee)
¼ cup medium fine ground coffee grounds freshly ground

Hazelnut Layers:

1 cup fine ground hazelnut flour almond can be used
¾ cup confectioner’s sugar
¼ cup all-purpose flour
3 eggs
1 egg yolk
3 egg whites
¼ cup fine sugar baker’s sugar
2 tablespoons melted butter

Soak:

3 tablespoons kahlua or coffee liquor

Assembly:

70 g dark chocolate

Instructions

Chocolate Ganache Icing:

To make the ganache, add chocolate, butter, salt, and vanilla into a bowl. Set aside
In a small pan over medium heat, heat cream and sugar until hot but just before boiling
Pour the heated cream and sugar over the bowl of chocolate and let it set for 1 minute. Stir until smooth
Set in the fridge until cooled but not hard

Cake:

Preheat the oven to 450 degrees fahrenheit
Add hazelnut flour (we make this with toasted, skinned hazelnuts that have cooled and been finely ground in the food processor), confectioner’s sugar, flour, eggs, and egg yolk into a medium bowl Beat for 1-2 minutes until combined
In a separate bowl, whip together the egg whites and sugar. Add egg whites and fine sugar into a medium bowl and whip until medium stiff peaks form
Fold into the hazelnut mixture to the egg whites
Fold in 2 tablespoons of melted butter
Line a 10 inches x 15 inches cookie sheet with parchment paper and spray with non-stick cooking spray
Add the batter into the pan and spread it in an even layer with an offset spatula
Bake until golden brown and the cake springs back to touch this will take about 7-10 minutes
Set aside to cool

Coffee Buttercream:

Cut the softened butter in tablespoon pieces.
Add 2 inches of water into a saucepan that fits the bowl of a stand mixer on top without touching the water. After the water is simmering, add the sugar, egg whites, and salt. Whisk to combine and continue to simmer, ensuring the water does not touch the bowl. Keep heating the mixture until the sugar is dissolved (it will be about 120 degrees)
Place the bowl in the stand mixer and whisk on high speed until mixture is thick and glossy. It should hold very stiff peaks.
Reduce the speed of the mixer to medium and add the butter one tablespoon at a time until incorporated. Reduce the speed to low and add the cooled coffee. Then add the coffee grounds. Turn up the speed to medium until well incorporated. Set aside
Note: this will make extra buttercream than needed for this cake

Assembly:

Trim the edges of the cake. Cut the rectangle into 3 even pieces each should be about 10 inches x 5 inches
Melt the 70 g of chocolate in the microwave or a double broiler. If using the microwave be sure to check and stir in 30 second increments
Place one piece onto a board or serving tray. Pour the melted chocolate on top and spread in an even layer so there is a thin layer of chocolate coating the entire cake. Allow the chocolate to harden
After the chocolate has hardened, flip over the layer so the chocolate becomes the bottom of the cake. Dab 1 tablespoon of kahlua evenly across the side of the sponge without the chocolate
Top with ~½ cup coffee buttercream and spread it into an even layer with an offset spatula
Top with another layer of the cake and dab 1 tablespoon of kahlua evenly across the sponge
Top with ~½ cup of chocolate ganache and spread it into an even layer with an offset spatula
Top with another layer of the cake and dab 1 tablespoon of kahlua evenly across the sponge.
Top with ~½ cup coffee buttercream and spread it into an even layer with an offset spatula. At this point set the cake in the fridge until it is hardened
After it has hardened, Top with ~½ cup of chocolate ganache and spread it into an even layer with an offset spatula
Optional use any remaining ganache to pipe on detail