The Great British Bake Off’s double chocolate swirled cake is sure to impress. Ask the Bakers what kind of cake they make for a birthday or other special occasion and almost inevitably they say chocolate – the richer and more eye-catching the better. This one ticks all the boxes. Dark and white chocolate mixtures are swirled together in the tins to make the sponge layers and these are sandwiched with a rum truffle ganache. The final, spectacular touch is the icing: dark chocolate ganache marbled with white chocolate. The cake tastes even richer if left for a day before cutting.
- For the sponge:
- 250g unsalted butter, softened
- 250g caster sugar
- 4 large eggs, at room temperature
- 1tsp vanilla extract
- 250g self-raising flour
- 75g dark chocolate (about 70% cocoa solids), roughly chopped
- 75g white chocolate (about 30% cocoa solids), roughly chopped
- 1tbsp cocoa powder
- good pinch of salt
- For the filling:
- 100g dark chocolate (about 70% cocoa solids), broken up
- 1tbsp dark rum
- 125ml whipping cream
- For the dark chocolate ganache:
- 150g dark chocolate (about 70% cocoa solids), broken up
- 150ml whipping cream
- For the white chocolate ganache:
- 75g white chocolate (about 30% cocoa solids), broken up
- 75ml whipping cream
Heat the oven to 180°C/350°F/gas 4. Put the soft butter into a large mixing bowl, or the bowl of a free-standing electric mixer, and beat with a wooden spoon or a hand-held electric whisk, or using the whisk attachment of the mixer, for a few minutes until creamy and mayonnaise-like. Gradually beat in the sugar and continue beating until the mixture turns pale and fluffy, scraping down the side of the bowl from time to time.
Beat the eggs with the vanilla extract just until combined, then gradually add to the creamed mixture, beating well after each addition. Add 1 tablespoon of the weighed flour with each of the last 2 portions of egg to prevent the mixture from curdling. Sift the rest of the flour and the salt into the bowl and gently fold in with a large metal spoon. Transfer half of the mixture to another bowl.
Gently melt the chopped dark chocolate. Leave to cool while you melt the white chocolate; cool this too.
Sift the cocoa into one bowl of cake mixture and add the cooled melted dark chocolate, then fold them in gently until thoroughly combined. Carefully fold the cooled melted white chocolate into the other bowl of cake mixture.
You want to put roughly half of the dark chocolate mixture and half of the white chocolate mixture into each of the prepared tins. Spoon the 2 mixtures alternately into the tins – a heaped tablespoonful of the dark chocolate mixture into each tin and then a heaped tablespoonful of the white chocolate mix into both tins. When you’ve finished, gently bang each tin on the worktop several times to settle the mixtures and eliminate any pockets of air. Carefully swirl a chopstick or table knife through the 2 mixtures in each tin to marble them.
Bake in the heated oven for 25–30 minutes until the sponges feel springy when gently pressed in the centre. For best results check the cakes after 20 minutes and rotate the tins to be sure the sponges bake evenly. Remove from the oven and set on a heatproof surface. Run a round-bladed knife around the inside of the tins to loosen the sponges, then turn out on to a wire rack and leave to cool completely.
When the cakes are cold, make the filling. Put the chocolate into a food processor and blitz to chop fairly finely. Stop the machine and add the rum. Heat the cream in a saucepan until it just comes to the boil, then, with the machine running, pour the cream into the processor through the feed tube. When the mixture is thick and smooth, scrape down the side of the processor bowl, then run the machine for a couple of minutes until the mixture is no longer warm. Transfer the mixture to a mixing bowl, or the bowl of a free-standing mixer, and whisk to the ribbon stage (*see note below).
Place one sponge layer crust-side down on a wire rack set over a baking sheet. Spread over the chocolate filling. Set the second sponge on top, crust-side up. Leave to set and firm up.
To make the dark chocolate ganache, put the chocolate in the food processor bowl and chop finely. Heat the cream until just boiling, then, with the machine running, pour into the processor bowl through the feed tube. Blitz until smooth. Scrape down the side of the bowl, then run the machine until the ganache is barely warm but still very fluid. Pour the ganache over the cake to cover it completely, using a palette knife if necessary to help ease the ganache down the side of the cake.
Working quickly, before the dark ganache has time to set, wash out the processor bowl and make the white chocolate ganache in the same way. Pour it into a jug and, if necessary, leave until it has thickened up but is still pourable – like double cream. Then, working across from one side of the cake to the other, pour the white ganache in thick stripes over the cake surface, allowing it to trickle down the sides. Gently draw a skewer along the stripes (not across them) to give a marbled appearance. Leave until firm and set before transferring to a cake board or serving plate. Store in an airtight container in a cool place – not the fridge – and eat within 5 days.
For this recipe you will need: 2 x 20.5cm round, deep sandwich tins, greased and base-lined