I have wanted to make an opera gateau for a while (before it was shown on the recent Great British Bake Off!) and thought my dad's birthday at the end of September would be a good opportunity. It strikes me as slightly more masculine somehow than a sponge cake - perhaps because of the dark chocolate and coffee colours, or the fact that the layers are (supposed to be) neat and precise - this is a cake without frills or fuss but that packs a lot of punch. In fact my mum said this was one of the best cakes she had ever had!
I found this recipe on the Marie Curie website ahead of their charity bake sale. I only found out afterwards that the sponge layers in an opera gateau should contain ground almonds and this recipe does not use any - I wonder perhaps if that is because many people are allergic to nuts and the charity wanted to make sure the recipes they suggested would be suitable for everyone. If I made it again I would try an opera gateau recipe with ground almonds, but nonetheless I was very pleased with the way this turned out. It is a little fiddly and takes a while to make but it is worth it.
For the sponge:
40g instant coffee granules (this is a lot so I was dubious but it worked)
85ml hot water
9 eggs, separated (again an awful lot and I was tempted to halve it, but don't - this makes enough to serve about 9 people and isn't actually as big a cake as you might think).
275g plain chocolate
185g caster sugar
For the coffee buttercream:
125g butter, softened
250g icing sugar, sifted
about 1-2 tbsp strong coffee (or use a dash of coffee extract)
For the chocolate ganache:
375g plain chocolate
500ml double cream
150g Nutella or similar
4 egg yolks
50g caster sugar
The recipe also included instructions for making a chocolate glaze for the top but I had enough of the ganache left that I used that on top instead.
First make the sponge layers. Preheat the oven to 180C and dissolve the coffee in the hot water in a large mixing bowl. Melt the chocolate in the microwave or a bain marie.
Separate the eggs and beat the yolks into the cooled coffee, and stir in the melted chocolate.
In a separate bowl, whisk the egg whites until you have stiff peaks then fold into the chocolate mixture.
I used a square tin for this recipe as when I have seen opera gateau it has been sliced into rectangles. You need to make three sponge cakes out of this mixture, and as I only have one square tin, I had to bake in three batches. Grease and line the tin and spoon a third of the cake mixture in; it will look shallow but it is supposed to.
Bake for about 10-12 minutes then turn onto a wire rack to cool. If you don't need to use the same tin again it is easier to leave the cake in the tin to cool; as it is thin it is quite fragile when it is only just cooked.
Meanwhile make the ganache. Use 210ml of the double cream and heat in a small pan. Break up the chocolate and add to the cream, stirring until it has melted - do not let the cream boil.
Beat the egg yolks and sugar together and add to the chocolate then whisk in the Nutella.
Whisk the rest of the double cream and then fold into the chocolate mixture. Set aside to cool, stirring occasionally until spreadable. I was a bit worried my ganache was too runny so I put it in the fridge for an hour before using.
To make the coffee buttercream, cream the butter and icing sugar together and add the coffee liquid and beat in.
Finally when the cake is cool you can assemble it. Do this on a cake board or serving plate as you won't want to pick up and move the cake once you have finished! Place one of your three cakes on the board as the bottom layer, and spread over half of the coffee buttercream. Then carefully spread over one third of the chocolate ganache.
I actually did this the other way around - ganache first, then buttercream, as suggested by the recipe, but my buttercream was a lot stiffer than the ganache which made it a bit difficult. Depending on how your ganache has turned out, you could do it either way around.
Gently place the next layer of sponge on top and repeat with the rest of the buttercream and another 1/3 of the ganache.
Place the last layer of sponge on top and spread with the remaining ganache.
I then refridgerated the whole thing overnight, as I knew it would have plenty of time to come back to room temperature the next day - we were driving from London to Southampton to have lunch with my family and then eating the cake in the afternoon.
I also decided it would be easier to slice into rectangles right after it came out of the fridge in the morning. It traveled really well and was absolutely delicious - worth the lengthy process!
Since then of course I have seen the Great British Bake Off where there were some great versions of an opera gateau, including the eventual winner Frances' Soap Opera gateau. Mine is more traditional but I was very happy with it!
I am sending this to Alphabakes - which I am hosting this month - as the letter I have chosen is O.