Passion Fruit and Mango Opera Cake

Good afternoon! I had a lot of fun with this bake. It looks difficult to get right on the show (because it is), but the results can be fantastic. This past weekend, I baked/created/sculpted the French opera cake. Traditionally, an opera cake is made with thin layers of coffee syrup-soaked jaconde sponge, coffee buttercream, and chocolate ganache. A la Great British Bake Off, I mixed it up a bit. I had a lot of fun going for mango syrup to soak my sponges with, passion fruit buttercream, and white chocolate ganache... and  I added two layers of mango jelly into the cake.

Creating the cake and all its elements was not tricky; the assembly and sculpting was the difficult part. For the ease of assembly, I tried to make all possible elements in the same 8" x 8" brownie pan. This made for a slightly smaller cake than those seen on the show, but it enabled me to have ample control over the end result (without too much cutting). When I tried to bake the sponge in a standard jelly roll pan (a lipped baking sheet), I was unable to spread the batter to all the edges while maintaining a thin enough layer. Using the same size pan for all elements was a lifesaver (not the hard candy).

The first step was to bake the sponge. A jaconde sponge is a very light sponge made with almond flour and using only whipped egg whites as a raising agent. The egg whites must be whipped with a tiny bit of granulated sugar until glossy stiff peaks form. Separately, the almond flour, confectioner's sugar, whole eggs, and vanilla extract must be mixed. The egg whites and melted butter must then both be carefully folded into the flour mixture. The mixture must be fully incorporated- there is nothing quite so nasty as a sponge cake with tiny pockets of scrambled egg whites- but the air should not be knocked out of the cake. The batter is enough to make five very thin cakes in an 8" x 8" pan. The cake only needs four, so there is an extra in case one rips (liable to happen). The cakes can be stored in the refrigerator or at room temperature with parchment paper separating the layers.

The next step is to make the mango jelly. In order to make the jelly vegetarian (and kosher), I used agar agar powder instead of gelatin. The mango jelly was very easy to make. I boiled some water with the agar agar, blended together mango and orange juice, poured the mango/orange juice puree into the gelatinous water, boiled, and then placed in the brownie tin (lined with parchment paper) to cool. Once it was cool, I sliced thin sections for cake assembly.

Then I made the mango syrup. In order to make the syrup, I simmered small mango chunks in sugar water for nearly an hour. I used a slightly under-ripe mango, so not that much mango flavor was imparted in the syrup; I remedied this by pureeing the mixture and sieving it to achieve my syrup. Once cool, the syrup was a bit thick. I would recommend making the syrup very shortly before assembly to prevent the need to cool it.

The passion fruit buttercream was fairly basic. Like any good buttercream, one has to cream together softened butter and confectioner's sugar. The main addition is the juice and pulp of at least three passion fruit. The juices can be attained from scooping out the interior of the fruit into a sieve and pressing the pulp through.

The last (and simplest) element is the white chocolate ganache. It is made by pouring simmering heavy whipping cream over white chocolate chips and stirring until incorporated. The ganache should be thick but spreadable for working with. The thick consistency prevents dripping and helps it set quickly, but it needs to be spread to the edges of the cake.

The assembly of the cake is a bit convoluted (I drew myself a diagram). It is key to get all of the elements in thin layers. If the cake layers are more than 3mm thick, I recommend carefully paring them down. The mango jelly must be cut down to size as well. The cooled mass of jelly should be enough for about four or five layers, but you only need to get two good ones. I found it useful to cut slices a bit thicker than the 3mm needed, and to then pare them down to the proper thickness. This method also enabled me to assure evenness in the slices. The actual order of the assembly will be listed in the instructions.

The cake turned out beautifully well. The layers were well-defined, and the tropical flavors were complementary but subtle.

Passion Fruit and Mango Opera Cake Recipe

Ingredients

Jaconde Sponge

6 large egg whites

2 tbsp granulated sugar

6 large eggs

2 C almond flour

2 1/4 C confectioner's sugar

1/2 C all purpose flour

1 tsp vanilla extract

3 tbsp unsalted butter, melted

Mango Jelly

4 small mangoes (500g)

juice of 2 oranges

2 1/2 C water

4 tsp agar agar

2/3 C granulated sugar

Mango Syrup

fruit of 2 small mangoes, finely diced

1 C water

3/4 C granulated sugar

Passion Fruit Buttercream

1 C unsalted butter, softened

3 C confectioner's sugar

juice and pulp of 4 passion fruit

White chocolate Ganache

3/4 C heavy whipping cream

1 lb. bag white chocolate chips

food coloring to taste

Instructions

1.    Preheat oven to 425°F (220°C). Line 8" x 8" brownie pan with parchment paper. Prepare extra sheets of parchment paper.

2.    To form jaconde sponge, whip egg whites until soft peaks form. Add granulated sugar and whip until glossy, stiff peaks form. Set egg whites aside. In a separate bowl, mix together whole eggs, almond flour, confectioner's sugar, all purpose flour, and vanilla extract. Gently fold in egg whites until incorporated. Gently fold in melted butter until incorporated. Be careful to maintain as much air as possible.

3.    Pour 1/5 of batter into pan. Bake 5-7 minutes until lightly brown. Immediately turn out of pan to cool. Line pan with new parchment paper. Repeat until you have 5 sponges.

4.    To form mango jelly, puree together mango and orange juice. Meanwhile, heat up water and agar agar powder in a small pot over low-medium heat until simmering. Stir mango/orange juice mixture into water. Stir until incorporated. Continue to heat until bubbling. Line 8" x 8" brownie pan with parchment paper and pour in jelly mixture. Refrigerate until semi-solid.

5.    To make mango syrup, finely dice fruit of 2 mangoes. Heat water and sugar in a medium saucepan over low-medium heat until simmering. Add mangoes. Let simmer 1 hour. Puree and strain through sieve to get syrup.

6.    To make passion fruit buttercream, cream together softened butter, confectioner's sugar, and heavy whipping cream. Gradually add in juice and pulp of 4 passion fruit through sieve and incorporate.

7.    To make white chocolate ganache, heat heavy whipping cream in small saucepan over low-medium heat until simmering. Pour over white chocolate chips, constantly mixing. If necessary, heat mixture in microwave 30 seconds until more liquid. Separate mixture into two equal portions. If desired, mix orange food coloring into one portion. This helps give visual distinction to the top layer (this cake is rather unfortunately pretty monochromatic with my chosen flavors).

8.    Assemble the cake. The bottom layer is one of the sponge cakes. Spread syrup over the entire top of the cake layer. Next, spread a thin layer of buttercream over the layer. Then place a layer of mango jelly on top of the buttercream. Coat the mango jelly with a thin brushing of mango syrup for sticking. Then place another layer of sponge on top of the jelly. Brush with syrup. Pour uncolored portion of white chocolate ganache over the sponge layer, and spread it all the way to the edges. Refrigerate until ganache is mostly set. Place another sponge layer on top of the ganache, and coat with syrup. Spread a thin layer of buttercream on top of the sponge. Place the second layer of mango jelly atop this buttercream, and thinly spread syrup on it. Place the last sponge layer on top of the jelly and coat with mango syrup. Spread one more thin layer of buttercream on top of the sponge and refrigerate 15 minutes until buttercream is firm. Remove cake from the fridge and pour colored ganache on top of it. Spread the ganache as close to the edges of the cake as possible and smooth it. Place cake in freezer at least 30 minutes. 

9.    Remove cake from freezer and trim all four sides so that all layers are neat and visible without awkward edges. Store in refrigerator or freezer until ready to serve.