Hazelnut chocolate opera cake

Hazelnut chocolate opera cake

By
From
B.I.Y. Bake It Yourself
Serves
10-12
Makes
1

This is proper showstopper territory: lots of techniques, lots of layers and lots of flavour. It’s great fun to make if you enjoy building things, as I do, and requires a steady hand and good attention to detail. Of all the things I make, this is the cake where people usually say ‘It’s a good job you’re a builder’, as it’s a bit like constructing a wall out of cake… using an offset palette knife instead of a trowel. Before you start this cake, make sure you can fit your cake tin on a shelf in the freezer.

Ingredients

Quantity Ingredient

For the praline

Quantity Ingredient
100g caster sugar
100g whole blanched hazelnuts

For the chocolate ganache

Quantity Ingredient
300ml double cream
300g dark chocolate, (70 per cent cocoa solids)

For the sponge

Quantity Ingredient
6 large eggs
100g caster sugar, plus more to sprinkle
a little bit vegetable oil, for the tin
100g plain flour

For the Italian meringue buttercream

Quantity Ingredient
180g caster sugar
3 large egg whites
300g unsalted butter, at room temperature
60ml hazelnut liqueur, (such as Fratello)

For the coffee syrup

Quantity Ingredient
4 teaspoons instant coffee
60ml coffee liqueur, (such as Kahlua)

Tool kit

Quantity Ingredient
baking tray
large piping bags
stand mixer fitted with whisk attachment
large swiss roll tin, (about 40 x 27 cm)
food processor
confectionery thermometer
pastry brush
18 cm square cake tin or adjustable cake tin, (this is a really useful tool)
offset palette knife
serving plate or cake board

Method

  1. Start by making the hazelnut praline. Pour the caster sugar into a heavy-based saucepan and heat gently. You may need to swirl the sugar around a bit to help it melt evenly, but try not to stir it. Once it has melted and taken on a very light yellow colour, tip the hazelnuts into the pan, take off the heat, and swirl around to cover all the nuts. If it thickens up too much to coat them, just heat up again to melt the sugar. Pour the coated hazelnuts on to a baking tray lined with baking parchment, scraping as much sugar out of the pan as possible, and set aside to cool completely. It will look at though you have ruined your pan forever. You haven’t. Just pour water in, heat it over the hob and the hardened caramel will dissolve.
  2. Next make the ganache, by first pouring the cream into a saucepan, then setting it on the hob to boil (yes, boil). Break the chocolate into a heatproof bowl and pour the boiling cream over. Stir with a silicone spatula until combined, dark and glossy. Pour three-quarters of this into a large piping bag and set aside to cool. Leave the remaining one-quarter in the bowl.
  3. Now for the sponge. Preheat the oven to 200°C. Put 3 eggs and 50 g of the caster sugar in the bowl of a stand mixer fitted with the whisk attachment and whisk until light-coloured and airy; this should take 5–7 minutes.
  4. Meanwhile, line the base of a lightly oiled large (about 40 x 27 cm) Swiss roll tin with baking parchment. Put the now-cooled praline into a food processor and blitz it to dust. Take 50 g of this and mix in a bowl with 50 g of the plain flour until all of the stuck-together lumps of praline have broken down. Reserve the remaining praline in an airtight container for the top of the cake. Using a silicone spatula, gently fold the flour mixture into the whisked egg mixture, making sure there is no dry stuff left in the bottom. Pour into the prepared tin and spread out with the spatula. Bake for 8 minutes, or until golden brown on top. (It will brown quickly, due to the praline.)
  5. Take out of the oven and leave to cool for 5 minutes, then sprinkle a fine layer of caster sugar on to a sheet of baking parchment. Tip the sponge on to this and peel off the baking parchment that it was cooked on (this will be a bit tricky, but be gentle and persevere). Repeat steps 3–5 to make a second sponge.
  6. For the buttercream, put 150 g of the caster sugar and 60 ml of water into a small saucepan with a cooking thermometer and set over a medium heat. Every now and again, brush down the sugar on the edges of the saucepan with a wet pastry brush. Do not stir! Meanwhile, beat the 3 egg whites with the remaining 30 g of caster sugar in the (cleaned) bowl of your stand mixer, on medium speed.
  7. Once the sugar on the hob reaches 110°C, set the stand mixer to high speed and beat the egg mixture until it reaches stiff peaks. Once the sugar reaches 118°C (‘soft ball’ stage), set the stand mixer to full power and slowly pour the sugar into the bowl, making sure not to pour it on to the moving whisk or you’ll just get hard sugar crusting on the sides. Keep the mixer running on full until the bowl has cooled down completely; this should take about 10 minutes so can be a bit noisy! While the mixture is cooling, chop the butter and add, chunk by chunk, to the cooled meringue (still on high speed). Once all the butter is combined, pour in the hazelnut liqueur, scrape down the sides of the bowl and load into a piping bag. Set aside, but do not put in the fridge or it will firm up too much to work with.
  8. Make the coffee syrup by mixing the instant coffee in a cup with 60 ml of boiling water and the coffee liqueur.
  9. To assemble, line an 18 cm square cake tin (or adjustable cake tin set at 18 cm) with cling film and cut the sponges into 4 x 18 cm squares. Carefully lay the first into the tin (making sure not to pull down the cling film) and use a pastry brush to soak it in one-quarter of the coffee syrup. Pipe one-third of the buttercream on top and smooth out with an offset palette knife. Freeze for 10 minutes to firm up.
  10. Remove from the freezer, pipe one-quarter of the ganache on top and smooth out with the offset palette knife.
  11. Repeat, building up the layers until everything is used up. (Though you will still have the one-quarter of the ganache that you set aside in the bowl earlier.) From the bottom it will be: syrup-brushed sponge > buttercream > ganache > syrup-brushed sponge > buttercream > ganache > syrup-brushed sponge > buttercream > ganache > syrup-brushed sponge. Return this to the freezer for about 1 hour to set.
  12. Take the cake out of the freezer and pour the remaining chocolate ganache from the bowl on top. Allow to set at room temperature.
  13. Remove the cake from the tin, peel off the cling film and (if you feel like it) cut about 5 mm off the edges to expose the sharp layers. You might as well show people the effort you have made…
  14. Transfer to a serving plate or cake board. Traditionally, these cakes have ‘opera’ piped on the top, but I like to sprinkle over the remaining praline in an even layer. Show off to anyone who stands still long enough.

Note

  • This recipe has a star bake (extra advanced) difficulty.

Extras

  • Fourteen steps, eh? Now, that is a long one! This cake is an absolute winner. All the components can be scaled up or down depending on what size cake you want to make with no difference in cooking time, so feel free to make a monster if you feel like it. I’ve made this with hazelnut liqueur, mainly because I try to find an excuse to put it in most things I make at the moment.

    There are a few pitfalls that you may encounter, so here’s how to repair the most common:

    The Italian meringue buttercream can sometimes split when you’re adding the butter (it will look like cottage cheese). To repair this, just take 3–4 tablespoons out of the mixture and microwave for 10–20 seconds, then return the melted liquid to the mixture, beating on high speed; this will get the buttercream back pretty much every time.

    You might find your ganache splits when you’re mixing in the cream. To remedy this, just whisk on a high speed until it re-combines.

    Other than those two fixes, this recipe should be plain sailing.
Tags:
Great British Bake Off
Baking
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