Chocolate Cube Cakes with Caramel (English)

A celebration cake of individual cake cubes, each with a delicious filling and stacked on an edible biscuit stand - this showstopping bake has something for everyone.

Joconde Sponge:
icing sugar (180 g)
ground almonds (180 g)
cocoa powder (25 g)
all-purpose flour, unbleached (55 g)
5 large eggs
unsalted butter, melted (45 g)
5 large egg whites (or use 150 g pasteurized egg whites)
golden caster sugar (45 g)

Mousse:
1 platinum-grade gelatine leaf
double cream (650 mL)
golden syrup (60 g)
54% dark chocolate, finely chopped (600 g)
ground roasted hazelnuts (100 g)

Caramel Filling:
granulated sugar (125 g)
double cream (140 mL)
54% dark chocolate, finely chopped (20 g)
milk chocolate, finely chopped (20 g)
white chocolate, finely chopped (20 g)

Biscuit Cake Stand:
unsalted butter, at room temperature (190 g)
golden caster sugar (150 g)
1½ tsp. coffee extract
1 Tbsp. instant coffee
golden syrup (130 g)
all-purpose flour, unbleached (580 g)
cocoa powder (60 g)
1 whole egg + 1 egg yolk, beaten
gold powder puff glitter dust
granulated sugar (100 g)

Decoration:
54% dark chocolate, finely chopped (350 g)
milk chocolate, finely chopped (350 g)
white chocolate, finely chopped (350 g)

Equipment:
26x36 cm Swiss roll tins x 2, each lined with baking paper
3 silicone trays of 5cm-cube dessert moulds
sugar thermometer
large disposable piping bag
4 baking trays, each lined with baking paper
20 cm square of baking paper, as a template
3 small disposable piping bags
18 cm squares of thin but strong cardboard or thin cake boards x 2, to support the biscuit cake stand

Preheat the oven to 415°F (210°C/190°C fan, Gas Mark 6-7).

Make the Sponge:
Place the icing sugar, ground almonds, cocoa and all-purpose flour, unbleached into a large bowl. Add the eggs and mix with a wooden spoon until smooth and thick. Stir in the melted butter.

Place the egg whites in a stand mixer fitted with the whisk attachment and whisk to soft peaks. Gradually add the sugar, continuously whisking on medium speed, until the mixture forms a meringue that holds stiff peaks.

One third at a time, fold the meringue into the chocolate batter, mixing well between each addition until the mixture is smooth and no streaks remain. Divide the mixture equally between the Swiss roll tins and use a palette knife to smooth out to an even thickness.

Bake the sponges for about 8-10 minutes, until just firm to the touch. Leave to cool in the tins, then turn out onto a wire rack and peel off the baking paper. Cut out 50 squares of sponge, each measuring 5 cm square.

Make the Mousse:
Place the gelatine in a bowl with 2 Tbsp. of water and leave soften. Pour 250 mL of the cream into a medium pan, add the syrup and heat to just below boiling point. Remove from the heat.

Remove the gelatine from the water and shake off the excess. Stir the gelatine into the cream mixture, then add the chocolate. Leave for 5 minutes, then stir well until the chocolate has melted. Leave to cool to 25°C on a sugar thermometer.

Place the remaining double cream into a mixing bowl and whisk until it forms soft peaks, then fold this into the chocolate mixture along with the ground hazelnuts. Place the mixture into the large piping bag and set aside.

Make the Caramel:
Place the sugar and 70 mL of water in a medium pan and cook on a medium heat until the sugar has dissolved. Increase the heat and boil for about 5 minutes without stirring until the syrup turns a golden amber colour. Gradually stir in the cream and boil for 1 minute, until the caramel is smooth and syrupy.

Place each type of chocolate in a medium bowl and pour one third of the caramel over each, stirring until the chocolate is melted. Leave to cool completely.

To Assemble the Cubes:
Place one square sponge in each of the square moulds (keep the top of the cake uppermost). Snip 1cm off the end of the piping bag. Pipe the chocolate mousse on top of the sponge around the inside of each mould, then fill the centre with 1 tsp. of caramel - fill 8 moulds with milk chocolate caramel, 8 with white chocolate caramel and the reminder with dark chocolate caramel. Then, pipe the remaining mousse on top, leaving enough height to press the top sponge onto the mousse.

Place the moulds in the freezer for at least 1 hour, or until the mousse is set and firm, then push each cube out of the mould and place the cubes in the fridge to chill until you're ready to decorate. (Don't leave them to freeze completely and don't attempt to coat them in chocolate if they are frozen.)

Make the Stand:
Place the butter, sugar, coffee extract and instant coffee powder into the bowl of a stand mixer fitted with the beater attachment. Beat for 3-4 minutes, until light and creamy, then beat in the golden syrup.

Sift the flour and cocoa into the bowl and add the eggs. Mix until the mixture clumps together into a soft dough. Turn out the dough onto the work surface and bring it together into a large rectangle about 4 cm thick. Wrap the dough in cling film and chill for 15 minutes to firm up.

Preheat the oven to 350°F (180°C/160°C fan, Gas Mark 4).

Divide the dough into 4 equal pieces. Remove one of the pieces of baking paper lining a baking tray. Roll out one piece of dough on top of it to about 5mm thick, then, using the 20cm baking-paper square template, cut a 20 cm square of dough. Repeat to make another two 20 cm squares. Discard the trimmings. Bake each square on the baking trays for 15 minutes, or until the biscuit feels firm. Remove from the oven and leave to cool.

To Make the Cake Stand Supports:
Roll the remaining quarter of dough to 5-6mm thick and cut it into eight 5 x 6cm rectangles. Place these on a lined baking tray and bake for 15 minutes, until firm. Remove from the oven and leave to cool.

Spray the baked and cooled large biscuit squares all over with gold glitter dust.

Decorate the Cakes:
Set aside 50g of each chocolate for the piping. Start with the dark chocolate. Place 150g of the remaining dark chocolate into a heatproof bowl and place the bowl over a pan of barely simmering water. Stir occasionally until melted and the chocolate reaches 45°C on the sugar thermometer. Add the remaining 150g of dark chocolate, stir and cool to 27°C. Return the bowl to the pan of simmering water and heat until the dark chocolate reaches 31°C.

Sit one cake cube on a fork and spoon over the melted chocolate to coat evenly on the top and sides, allowing the excess melted chocolate to drip back into the bowl. Carefully place the cube on a cooling rack and repeat until you have coated 8 cakes in dark chocolate.

Repeat steps 18 and 19 for the milk and white chocolates, tempering them to 29°C (rather than 31°C).

Melt the remaining 50 g of each chocolate separately as before, then place each in a small, disposable piping bag. Snip the ends and pipe dark chocolate over 4 of the white cubes and 4 of the milk chocolate cubes. Pipe milk chocolate over 4 of the dark cubes and 4 of the white cubes. Pipe white chocolate over 4 of the dark cubes and 4 of the milk cubes. Set aside to set.

Assemble:
Place the 100 g of granulated sugar in a small pan over a medium heat and cook without stirring until the sugar starts to caramelise around the edge of the pan. Shake the pan occasionally until all the sugar has turned a deep golden brown, then remove from the heat.

Dip 3 sides of each biscuit rectangle, one at a time, in the caramel, being very careful not to get caramel on your fingers. Place the short side of one biscuit in the centre of one square gold biscuit, and place another 3 rectangles against one another to make a box support in the centre of the cake stand. Leave to set. Repeat with the second tier. Do not glue the tiers of the stand together. Remember to place the thick cardboard under the biscuit plates to support the weight of the cakes. Finally, arrange the cakes onto the biscuit tiers and layer them up just before serving.

Makes 24.