Salted mocha Opera cake

Multiple layers of liqueur-kissed almond sponge cake, salted mocha buttercream and chocolate ganache: very much a cake for when a special treat is needed. And with elements that can all be made in advance, this becomes a matter of gentle assembly rather than frantically using a whole day or so in the kitchen!

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I adore gâteau opéra and if I ever get the chance to eat it when I am out then I will leap at that chance hungrily!

While the coffee and chocolate flavour remains top of my opera cake loves, I am very partial to a strawberry and passion fruit version: rich, creamy and so wonderfully tangy.

For this cake I have salted the buttercream a little: not too much, just enough to wake up the taste buds. Think salted caramel! But the salt can be omitted if you are not a fan of it.

The cake is best served slightly at room temperature: remove the cake from the fridge for about 30 minutes to give the buttercream a chance to soften and you have the most incredible melt-in-the-mouth sensation.

It’s all about the layers

The trick with a layered cake such as the gâteau opéra is getting the layers firm enough before you add the next layer so that you can get clearly defined layers.

The freezer is your best friend here for firming up the layers as you go.

The assembled cake then gets chilled to firm up fully, making it easy to cut cleanly with a long, shape knife that has been dipped in hot water.

A cake frame: a very useful implement!

I love my rectangular frame. It is ideal for layered cakes and desserts, keeping everything in place during the assembly so that you simply lift off the ring at the end to reveal what is hopefully a spectacular layered marvel.

But if you don’t have a cake frame….

Fear not! You can simply stack the layers as you go on a flat surface such as a baking tray.

Or layer up the cake in a deep loose-bottomed cake tin, with a sheet of greaseproof around the inside to help it come out of the tin at the end.

While the buttercream and ganache are soft, they are not at all runny, so it is easy to layer up. The freezing (or, if you have more time, the chilling in the fridge) at various stages ensures enough rigidity to maintain stable layers.

Great news: the elements can be made in advance!

When I make a cake such as this, I rarely make it all in one go. I like to make up the separate components ahead of time, at my leisure, so that when I am ready to finish the cake it is simply about assembling the different layers.

With this gateau, there are three main elements in addition to the sponge: the syrup, the buttercream and the ganache. I occasionally make a chocolate mirror glaze for the top, but I do like the matt finish that I have gone for here.

Buttercream:

Can be made several days ahead and left covered in the fridge. Simply remove a few hours before you want to assemble the cake so that the buttercream is soft enough to spread.

Ganache:

Can also be made several days and left covered in the fridge. gently heat it in the microwave just until it softens enough to be able to be spread easily.

Syrup:

Will keep for ages in the fridge in a screwtop jar

The approximate timings for each element

• sponge: up to 20 minutes to make and bake it
• buttercream: 20 minutes to make
• ganache: 10 minutes to make
• coffee syrup: under 5 minutes to make
• assembly: 20-30 minutes hands-on time, plus time to freeze

Recipe: salted mocha Opera cake – serves 12 generously

sponge

• 4 large egg whites (the yolks will be used in the buttercream)
• 4 large whole eggs
• 160g caster sugar
• 140g ground almonds (or use pistachios, walnuts or a mixture)
• 40g plain flour, sifted
• 30g unsalted butter, melted and cooled
• generous pinch of sea salt

Salted mocha Buttercream

• 4 free-range egg yolks
• 1 whole egg
• 100ml water
• 2 teaspoons coffee granules
• 200g caster sugar
• 400g butter
• 1/2 teaspoon fine sea salt
• 100g white chocolate, melted and cooled
• 3-4 tablespoons cooled espresso coffee

Chocolate Ganache

• 180ml double cream
• 100ml milk
• 300g dark chocolate, chopped fairly small
• 150g milk chocolate, chopped fairly small
• 50g unsalted butter, softened
• 3 tablespoons espresso coffee
• 1/2 teaspoon fine sea salt
• 3-4 tablespoons cold milk*

*might not be needed, but storring in cold milk will rescue the ganache if it starts to split/curdle

to brush over sponge

• about 100ml hot espresso
• 2 tablespoons caster sugar
• about 50ml alcohol of choice: rum, brandy, Tia Maria, Marsala…..

To finish (optional)

• cocoa powder or
• melted white chocolate or
• chocolate curls/shavings

You will also need:

• 3 small Swiss roll tins (about 30cm by 20cm) buttered and lined with parchment or greaseproof
  
• a baking sheet lined with parchment for placing the cake on as you layer it up
• a rectangular cake frame (ideal but not essential)
• an electric hand whisk or a food mixer with the whisk attachment

Make the sponge

(1) Preheat the oven to 170°C(fan). Put the egg whites, salt and half of the sugar in bowl and whisk on a high setting in a food mixer until you get stiff peaks: you could also use a hand-held electric whisk.

(2) Add the whole eggs, one at a time, and with the setting on high whisk for 2-3 minutes or until the mixture has increased even more in volume and is very light textured: at this stage the mixture always reminds me of a very airy foam!

(3) Gently fold in the ground nuts, flour and the rest of the sugar. Pour the melted butter down the edge and fold in. Go right to the bottom of the bowl and around the edges to ensure you incorporate every bit of butter.

(4) Spread the mixture thinly and evenly onto the prepared tins, making sure the mixture gets into the corners.

(5) Bake in the preheated oven for 7 minutes until the tops have only just taken on a light golden colour.

(6) Leave to cool in their tins before turning out onto a large sheet of greaeproof dusted with caster sugar, which prevents the sponge from sticking to the paper.

NB: the cooled sponges can be wrapped in clingfilm and frozen until needed if preferred.

Make the buttercream

(1) To make the coffee buttercream, add the caster sugar, the coffee granules and the water to a medium pan and heat over a low heat, stirring to dissolve the sugar.

(2) Increase the heat and bring to the boil. Once boiling, reduce the heat a little and simmer until a thick syrup is produced. The mixture will bubble up somewhat but don’t be alarmed: just keep an eye on it so it doesn’t bubble over. This takes about 5 minutes. If using a thermometer, go for 110°C.

NB: I have made this buttercream countless times, usually without thermometer, letting the syrup boil for about 5 minutes. As long as the syrup is past boiling temperature, it will be hot enough to cook out the eggs.

(3) Place the egg and egg yolks in the food mixer bowl bowl and whisk together for a few moments. Slowly pour the hot syrup into the egg mixture while still whisking on a high setting until you have a light, mousse-like mixture that holds it shape, like softly whipped cream:

NB: it might not look as if it is going to thicken, but it will do. I usually go for about 5-6 minutes, by which time the mixture has also cooled down.

(4) With the mixer on high, add the butter a little at a time into the cooled mixture, until it has been incorporated fully. Whisk in the salt and about half of the chocolate. Asd the espresso, a little at a time, and whisk until fully incorporated. Whisk in the rest of the chocolate to give a smooth, luscious buttercream.

NB: the chocolate also ensures the buttercream will not curdle when the espresso is added.

Make the ganache

(1) Put the coffee, cream, milk and salt into a small pan and bring to the boil. Once it boils remove from the heat and leave for a few minutes.

(2) Put the chocolates and butter into a medium bowl. Pour over the cream and leave it alone for a couple of minutes until the chocolate has started to melt.

(3) Now slowly stir the mixture until the chocolate has fully melted and you have a smooth, glossy mixture. If the mixture starts to split, simply stir a couple of tablespoons of cold milk and it should come back together. Cover with clingfilm until needed.

Prepare the coffee liqueur to brush over

(1) Dissolve the sugar in the espresso and stir in the alcohol. That’s it!

Assemble the cake:

This is the most exciting part now that the main work has been done. I adore seeing the cake build up.

(1) Have the liqueur syrup, the buttercream and the ganache to hand. Invert the cakes onto a sheet of parchment dusted with caster sugar, carefully peel off the paper from the cakes.

(2) Brush each sponge generously with the liqueur syrup. If using a frame, use it to cut out the cake to give 3 idential “sheets” of cake that will fit the frame snugly.

(3) Put the cake frame on baking tray lined with greaseproof: make sure the baking tray will fit in the freezer, although the fridge will be fine as an alternative.

(4) You now layer up the cake on top of this sponge base, freezing for 10 minutes or so after the buttercream is spread over each time:

• put one of the sponge layer in base of ring
• spoon over half the buttercream and smooth off
• freeze for 10 minutes or refrigerate for half an hour
• spoon over 1/4 of the ganache and smooth off
• put the second sponge on top and pat down lightly
• spoon over the rest of buttercream and smooth off
• freeze for 10 minutes or refrigerate for half an hour
• spoon over another 1/4 of the original ganache and smooth off
• put the final sponge layer on top and pat down lightly
• spoon over just over half of the remaining ganache and smooth off
• chill for several hours or overnight

(5) The next day, heat the rest of the ganache very gently in the microwave just until it becomes runny. Leave to cool but not set.

(6) Run a palette knife around the inside of the cake frame and lift off the frame.

(7) Pour over the runny ganache and use a palette knife to smooth it out. You can give the cake a gentle shake to help if needed. Chill for about 30 minutes to set.

(8) Trim the edges with a long sharp knife that has been dipped in hot water and then wiped dry: enjoy these trimmings; it’s the baker’s privilege! Cut the cake into equal slices, either square or rectangular, wiping the knife after each cut to give clean slices. Go for 10-12 slices for generous portions or else cut into small squares if preferred.

NB: I sometimes pop some of these pieces back into the freezer in an airtight container, taking out just what I want whenever the craving hits me at a later time!

(9) Decorate however you wish: melted white chocolate, chocolate shavings, a dusting of cocoa powder…..or even nothing at all! Refrigerate and remove from the fridge about 30 minutes before you want to eat a piece so that the buttercream and ganache have softened slightly.