Gateau Opera

A classic of French Patisserie yet equally at home as part of an English afternoon tea: Gateau Opera is a layered cake of coffee and chocolatey wonderfulness.

The cake layers are made of joconde sponge, also known as joconde biscuit. This is an almond based sponge which is lightened with whipped egg whites. The texture is soft but it doesn’t crumble which keeps the slices perfectly neat when cut.



I was slightly nervous about attempting French buttercream: it requires you to beat hot sugar syrup into whipped egg yolks, which I imagined resulting in third degree burns and scramble eggs, but it actually turned out fine!

Don’t be put off by the number of stages to the recipe, none of them take very long to do and you can spread it out over a couple of days, for example by making the joconde, coffee syrup and coffee buttercream on one day then making the chocolate ganache and glaze and assembling it the next.



Things I have learnt from making Gateau Opera:

I have had such difficulties with making caramel from a mix of sugar and water, rather than the sugar only method which seems much more reliable. After many attempts this weekend I have found it works best if you tip the sugar into a pile in the middle of the pan and pour the water on the middle of the sugar. This way the water will spread evenly throughout the sugar without the need to even touch the pan, and definitely no need to stir it, which you must NEVER do.

I didn’t use a thermometer to test the temperature of the sugar syrup. It’s easy enough to test that its reached ‘soft ball’ stage by using a teaspoon to drop small amounts into a measuring jug of cold water. Once it forms a ball of sugar that is pliable it’s ready to whisk into the eggs.

Take your time when cutting the slices – it makes such a huge difference to the look of the finished gateau. After each cut wash the knife in hot soapy water, then rinse and dry on clean tea towel. You know you will kick yourself afterwards if you skip this step and get crumbs in your shiny shiny chocolate glaze.



Gateau Opera: makes 6-8 slices
(adapted from Joe Pastry’s recipe over here)

Joconde sponge:
15g caster sugar
115g ground almonds
115g icing sugar
35g plain flour
3 whole eggs
3 egg whites
20g butter, melted, plus extra for greasing the baking tray

• Preheat oven to 200°C
• Line the base of a 10 x 15 baking tray with parchment and brush melted butter over the base and sides
• Beat the egg whites on a low speed until soft peak stage then gradually add the sugar and increase the speed, continuing to beat until a stiff meringue is formed.
• In another mixing bowl beat together the almonds, icing sugar and whole eggs until pale and increased in volume, then mix in the flour.
• Fold in the meringue, a quarter at a time, until just incorporated then lastly fold in the melted butter
• Pour the batter into the prepared baking tray, spreading it out into a thin, even layer
• Bake in the oven for 6-7 minutes
• Once cooked, turn out of the pan onto a layer of parchment
• Peel the parchment from what is now the top of the turned out sponge and leave until cool

Coffee syrup:
½ cup sugar
¼ cup water
1 ½ teaspoons of instant coffee granules

• Put all the ingredients in a pan and bring to a simmer over a medium/low heat
• Leave to cool before using

Coffee buttercream:
3 egg yolks, at room temperature
½ cup sugar
1/8 cup water
225g butter, cut into 2cm cubes
1 teaspoon instant coffee granules

• Mix the coffee granules with 1 teaspoon of boiling water and set aside to cool
• Whisk the egg yolks to a pale, frothy consistency in a large mixing bowl
• Put the sugar and water in a pan and bring to a simmer over a medium/low heat
• DO NOT STIR THE SUGAR SYRUP! (see notes above)
• Once all the sugar syrup reaches ‘soft ball’ stage (or 120°C/248°F if using a sugar thermometer) it is ready to be added to the egg yolks
• Pour small amounts of the sugar syrup down the inside of the bowl so it doesn’t land directly on the egg yolks, whisking with electric beaters between each small addition, until you have added all of the syrup
• Keep whisking the mixture until it has cooled to room temperature (it’s important that it is not any hotter as it will cause the butter curdle)
• Start adding the butter one cube at a time, beating until fully incorporated before adding the next
• The buttercream should now be silky-smooth and wonderfully creamy
• Mix in the cooled coffee

Chocolate ganache:
100g dark chocolate (70%)
150ml double cream

• Break the chocolate into squares and place in a microwavable bowl along with the cream
• Heat in the microwave for short bursts, stirring well between each burst, to form a smooth ganache

Chocolate glaze:
30g cocoa powder
60ml double cream
90g caster sugar
4g of sheet gelatine

• Place the gelatine in a bowl of cold water and leave to soak
• Put the cocoa, cream, sugar and 75ml of water in a saucepan and bring to the boil over a medium heat, stirring continuously
• Keep this mixture at a gentle simmer for a further 5 minutes whilst stirring
• Remove from the heat, squeeze the excess water out of the gelatine and add it to the cocoa mixture. Stir thoroughly ensuring that there are no lumps of gelatine remaining
• Leave to cool to 35°C (roughly body temperature, so it should feel neither warm nor cold to the touch) before using
• If it gets too cold you can re-warm it in the microwave for a few seconds

Assembling the Gateau Opera:

• Brush the coffee syrup over the joconde sponge layer
• Cut the sponge into 3 equally sized pieces
• Spread the coffee buttercream over one piece of sponge in an even layer about ¼ inch thick
• Spread a thin, even layer of chocolate ganache over another piece of sponge (this will be the top layer) and then spread the rest of the ganache over the last sponge rectangle
• Place the coffee sponge layer on top of the thick chocolate ganache followed by the top layer
• Leave in the fridge for ½ an hour for the ganache to set, then pour a thin covering of the chocolate glaze over the top of the gateau
• Place in the fridge for at least 4 hours or overnight
• Once the glaze has set, remove from the fridge and cut into neat rectangles with a large knife, washing and drying the knife between each cut
• Decorate with gold leaf (if you can bear to part with £4.25 for a teeny tiny pot!) or gold sprinkles
• The finished gateau will keep in the fridge for another day or so, and should be allowed to come to room temperature before serving