Opera Gateau: coffee, chocolate & rum flavour

The last time I made an Opera Gateau I went for layers of sponge brushed with lime syrup and rum, ginger & lemongrass buttercream and passionfruit with white chocolate ganache: this time I went for the more classic Opera Gateau using layers of coffee & rum soaked sponge, coffee buttercream and dark chocolate ganache.

It is a few years since I last made an Opera Gateau so I felt it was time to re-visit this classic cake.

I would normally make a rectangular Opera Gateau but I could not for the life of me find any of my rectangular loose-bottomed tins: last seen before I moved house! A rectangular cake cut into very small squares makes excellent petits fours.

The recipe is a slight variation on the traditional joconde sponges: this time I used hazelnuts for a slightly different flavour to the sponge rather than almonds.

Opera gateau
Opera gateau

Pailleté feuilletine layers:

I like a bit of crunch, so I added a little pailleté feuilletine, which I mixed with some melted chocolate and praline paste, leaving it to set before crumbling it and adding it to a few of the layers. The pailletés feuilletines (“small flaky leaves”) are essentially very thin, crunchy tuiles. You can buy pailleté feuilletine from kitchen stockists although they are easy to make (recipe below).

Roughly crushed cornflakes or rice crispies mixed with melted chocolate and praline paste gives an acceptable substitute: it isn’t quite the same but it’s easy and it works well enough.

Preparing ahead:

The trick with an Opera Gateau is getting all the component parts prepared, and most of these can be prepared ahead of time: the recipe for each is given below.

The sponge can be frozen beforehand and the ganache is made in moments, needing only a little time to firm up a little in the fridge. The pailletés feuilletines can be made ahead and stored in an airtight container to keep them crisp: if they go a little soft, scatter them over a baking sheet and re-bake for a couple of minutes before cooling, after which they will crisp up again.

The only challenging part is the buttercream, which is made with boiling sugar syrup whisked into eggs: this approach gives a wonderfully light, moussey buttercream but that can be made up in about 10 minutes or so. I have made buttercreams this way using yolks and sometimes using just the whites but to be honest, using the whole egg works a dream and, of course, the hot sugar syrup cooks the eggs.

If making the buttercream or ganache ahead of time, remove them from the fridge to soften somewhat before beating well so that they are easy to use.

A fun word of caution:

Check the bottom of the loose-bottom tin you use for the layering is, in fact, loose enough: the one I used this time (a new tin!) stuck somewhat as it was meant to pop out of the top and needed a bit of force for it to completely come out. I’ve done this so many times with cakes in the past so this was an intriguing issue for me! As a result, the cake slid off onto the work surface!  Thankfully the main bulk of the cake had been well chilled and the only slight damage was to the top layer which wrinkled a bit.

Opera Gateau: makes one 7″ cake

The individual components:

The joconde sponge:

  • 120g egg whites (about 3 large eggs whites), at room temperature
  • 20g caster sugar
  • 150g ground hazelnuts
  • 150g icing sugar
  • 2 large eggs, at room temperature
  • 40g self-raising flour
  • 25g unsalted butter, melted

(1) Line two large baking sheets with baking parchment or silicone sheets and preheat the oven to 200C(fan). In a clean mixing bowl whisk the egg whites and the caster sugar until they form firm, glossy peeks. Set aside this meringue (for it is vaguely a meringue!).

(2) Sift the ground almonds and icing sugar into a bowl and add the eggs. Whisk for several minutes until it becomes fairly pale and thick. Fold in the flour gently.

(3) Fold about 1/3 of the meringue into to the almond mixture to lighten it. Fold in the remaining meringue gently.

(4) Pour the melted butter slowly down one edge of the bowl and fold in gently until you see no more streaks of butter. Pour into the two tins and smooth out. Bake for 6-7 minutes. Don’t over-bake the sponge: it should be pale with barely a hint of colour. Leave to cool in the tins.

Pailleté feuilletine (makes more than is needed):

  • 50g unsalted butter, softened
  • 30g icing sugar
  • 20g soft brown sugar
  • 50g egg white, at room temperature
  • 50g plain flour
  • 25g milk chocolate, melted
  • 20g praline paste

(1) Beat the butter, sugars, egg white and flour together until very smooth. Spread a few spoonfuls as thinly as possible onto silicon sheets and bake in an oven preheated to 180C(fan) for about 5 minutes until golden brown. Cool on the sheets and then crush roughly into flakes. NB: it is best doing this in batches. I have also frozen the raw mixture to use at a later time, which gives excellent results.

(2) Mix about 60g of the flakes with the chocolate and the praline paste. Spread out onto a baking sheet or large plate and allow to set. Once set, roughly crush. Store the remaining flakes in an airtight container.

Chocolate ganache:

  • 100ml full-cream milk
  • 100ml double cream
  • 300ml best quality dark chocolate, roughly chopped
  • pinch fine sea salt
  • 2 teaspoons very strong espresso coffee
  • 40g unsalted butter, softened

Put the chocolate in a bowl. Put the milk and the cream in a small pan and bring to the boil. Pour over the chocolate and mix well until the chocolate has melted. Add the butter, sea salt and espresso and stir well until you get a smooth glossy mixture.

NB: You don’t have to use salt and coffee but they bring out the chocolate flavour wonderfully without dominating the chocolate flavour. Instead of espresso, dissolve several teaspoons of instant coffee with a little water: this coffee liquid can also be used with the buttercream.

Coffee buttercream:

  • 225g caster sugar
  • 40ml water
  • 2 large eggs, at room temperature
  • 225g unsalted butter, softened
  • 4 tablespoons very strong espresso coffee

(1) Put the sugar and water in a small pan and bring slowly to the boil, shaking the pan occasionally to help dissolve the sugar. Allow it to reach 120C, although boilin or about 5 minutes until it become a little syrupy will be fine.

(2) Put the egg yolks in a mixing bowl and whisk for a few moments. Slowly pour over the hot sugar syrup, with the whisk on full speed, and whisk for about 5 minutes or so until you have a very light, pale mixture. Leave to cool and then whsk in the butter until well incorporated. With the whisk on, add the coffee a little at a time until fully incorporated.

Chocolate glaze: (to be made when the cake has been layered up)

  • 80g best quality dark chocolate
  • 30g unsalted butter, softened

Melt the chocolate and mix in the butter until incoproaated.

Coffee syrup (for brushing over the sponge):

  • 10g caster sugar
  • 6 tablespoons very strong espresso coffee
  • 4 tablespoons dark rum or brandy

Mix the ingredients together until the sugar has dissolved.

Assembling the Opera Gateau

With all the compoents made the assembly of the gateau is an easy part of the process. You can chill the cake for about 10 minutes or so after each layer is placed if the filling seems a little soft.

(1) Line the inner circumference of a loose-bottomed tin with acetate.

(2) Invert the sponge onto a work surface that is very lightly dusted with icing sugar (to stop the sponge from sticking). Peel off the parchment or silicon carefully. Cut out circles that are the size of the tin. For a 7″ cake you should be able to get four whole circles and then two semi-circles ie) 5 sponge layers in total, but for an 8″ cake you can get four 8″ layers with a bit of patchworking (which really does not affect the overall cake and nobody will know!).

(3) Put one of the sponge discs into the bottom of the tin and brush liberally with the coffee syrup. If the sponge is a bit too big, just push it a bit to fit. Sprinkle over a little of the paillete feuilletine.

(4) Put a few tablespoons of the coffee buttercream over the sponge layer and smooth out.

(5) Put a second layer of sponge over the buttercream and brush liberally with the coffee syrup.

(6) Put a few tablespoons of the ganache over the sponge layer and smooth out.

(7) Repeat until all of the sponge layers have been used, sprinkling the paillete feuilletine every few layers or so. Spread some coffee buttercream over the top followed by a little ganache. Chill for about 10 minutes and make the chocolate glaze.

(8) Pour the chocolate glaze over the cake and smooth it off: gently shaking the tin is easiest.

(9) Decorate in any way you wish (drizzling chocolate over it, for example, or edible gold leaf).

(10) Lift the cake out of the tin (lay the base on a cup or a tin to push the base upwards) and carefully remove the acetate.

 

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Author: Philip

Very much into baking and general cooking.