Two 20 cm (8 inch) round cakes (we used chocolate cake, but you could use mud cake)
White chocolate buttercream
4 tablespoons cream
150 g (5 oz) white chocolate melts
200 g (6.5 oz) unsalted butter
80 g icing sugar
80 g milk chocolate
125 ml (4 fl oz) cream
80 g (23/4 oz) dark chocolate
80 g (2 3/4 oz) white chocolate
200 g (6 1/2 oz) flaked almonds, toasted
1 - To make the white chocolate buttercream, put the cream and chocolate in a small heatproof bowl. Bring a small pan of water to a simmer, remove from the heat and place the bowl over the pan (don't let the bottom of the bowl sit in the water). Stir the chocolate over the hot water until melted, then remove from the heat and leave to cool. Chop the butter and beat until light and creamy, then gradually beat in the sugar until thick and white. Beat in the melted chocolate until the mixture is thick and fluffy.
2 - Using a serrated knife, cut each cake horizontally into 3 even layers
(trim away the domed top, if necessary). Place a layer of cake on a wire rack over a tray and spread with a sixth of the buttercream. Top with another layer of cake, spread that with buttercream and build up the layers, sandwiching the cake and filling. Finish with a layer of cake, cut-side-down to give a flat surface (keep the remaining portion of buttercream). Refrigerate the cake for 30 minutes to firm the filling, so that the layers don't slide apart.
3 - Put the milk chocolate in a small heatproof bowl with 2 tablespoons of the cream. Bring a small pan of water to a simmer, remove from the heat and place the bowl over the pan (don't let the bottom of the bowl sit in the water). Stir the chocolate and cream over the hot water until melted and blended. Alternatively, melt in the microwave for 1 minute on High, stirring after 30 seconds. Do the same with the dark chocolate and white chocolate, blending each with 2 tablespoons cream so you have three separate chocolate mixtures.
4 - Spoon dollops of each chocolate mixture randomly over the top of the cake and then swirl them together with the thick end of a skewer to create a marbling effect. Gently tap the tray on the bench to level the icing. Leave to set, then remove any drips of icing from down the side of the cake and spread the remaining buttercream around the side. Roughly crush the almonds and press over the buttercream. Transfer the cake to a serving plate or stand.
Stand the cake on a rack over a tray and build up layers of cake and buttercream.
Melt the three chocolates separately and then dollop over the top of the cake.
Gently swirl together the colored chocolates, to give a marbled effect.
Ahead of time: This cake can be stored in the fridge for up to 3 days after decorating. Bring to room temperature before serving.