Chocolate marble cake

This spectacular creation is definitely worth the effort.

MAKES 24 slices

PREPARATION TIME 1 hour 40 minutes, plus cooling and chilling

COOKING TIME about 1 hour 45 minutes

FOR THE VANILLA SPONGE

350g unsalted butter, softened, plus extra to grease

600g caster sugar

475g plain flour

½tsp baking powder

¼tsp bicarbonate of soda

8 large eggs, at room temperature 1½tsp vanilla extract

250ml sour cream

FOR THE CHOCOLATE SPONGE 275g plain flour

1tsp baking powder

½tsp bicarbonate of soda

75g cocoa powder

350g caster sugar

250g unsalted butter, softened 175ml sour cream

2 large eggs, plus 2 large egg yolks 1½tsp vanilla extract

FOR THE BUTTERCREAM

350g dark 70% chocolate, broken into pieces

6 large egg whites

300g icing sugar, sifted

400g unsalted butter, softened FOR THE SHARDS

75g each dark and white chocolate FOR THE GLAZE

125g dark chocolate, finely chopped 75g unsalted butter, softened FOR DECORATION

Chocolate truffles

1 Preheat oven to 180°C (160°C fan) mark 4. Lightly grease and line 3 x 20cm cake tins, at least 10cm deep,

with baking parchment.

2 Begin by making vanilla sponge. In a large bowl, cream butter and sugar with an electric whisk for about 5min until light and fluffy. Into a medium bowl, sift flour, baking powder and bicarbonate of soda; add ¾tsp salt.

In a large jug, beat eggs, vanilla extract and sour cream. Set all mixtures aside.

3 For chocolate sponge, in a large bowl, sift flour, baking powder, bicarbonate of soda and cocoa. Stir through sugar and ¾tsp salt. Add butter and beat gently with an electric whisk until mixture looks like wet sand. In a large jug, beat together sour cream, eggs, yolks and vanilla until smooth. Set mixtures aside, separate from vanilla sponge mixtures.

4 Finish the vanilla sponge. Gently beat a third of the flour mixture into creamed butter mixture, followed by half the sour

cream mixture. Repeat with another third of flour, remaining sour cream and final third of flour, folding until smooth. Set aside.

5 Finish chocolate sponge. Gradually add the sour cream mixture and 100ml boiling water into flour mixture; beat until smooth.

6 Divide the vanilla and chocolate sponge mixtures among 3 cake tins, adding them in alternate spoonfuls. Swirl together with a palette knife (for best marble effect, don’t overmix). Bake in middle of oven for 1hr 10min-1hr 15min until springy to touch. Leave to cool in tins for 10min, then turn out on to a wire rack to cool completely. Remove parchment and trim tops off sponges so cakes are 5cm deep.

7 For the buttercream, melt chocolate in a large bowl over a pan of barely simmering water. Remove from heat and set aside to cool for about 20min. Put egg whites in a large bowl with icing sugar and stir to combine. Set bowl over same pan of water and increase heat slightly so it is simmering gently. Beat with an electric whisk for about 5min until thick and stiff like meringue, and a teaspoon stands upright in mixture. Remove from heat, then whisk for 10min until completely cooled, thick and stiff. Whisk butter into cooled, melted chocolate. Gradually add chocolate mixture to meringue, whisking until light and fluffy.

If it looks like it is going to split, cool in fridge for up to 15min. Beat again until smooth.

8 Put the bottom layer on a 20cm round cake board; spread with buttercream. Add second and third layers, sandwiching them together with buttercream, and turning top layer upside down to give the cake a flat surface. Spread remaining buttercream over top and sides of the cake with a palette knife. Chill for 30min.

9 For the chocolate shards, gently melt dark and white chocolate in separate bowls over pans of simmering water. On a baking sheet lined with baking parchment, pour dark chocolate in a thin layer (about 3mm thick). Spoon white chocolate on to dark layer; swirl together with a spatula (don’t overmix), tilting tray to ensure surface sets evenly. Set aside.

10 For the glaze, put chocolate and butter in a medium bowl set over a pan of barely simmering water. Stir until melted. Pour over the cake, smoothing the top with a clean palette knife and encouraging it to drip over the edges. Decorate with chocolate shards and truffles. Chill to set. Remove 2hr before serving. Store in the fridge for up to 2 days.