Triple chocolate layer cake

Preheat the oven to 190˚C, gas mark 5. Grease and line 3 x 18cm sandwich tins; set aside. Put 150g chocolate in a heatproof bowl over a pan of barely simmering water, ensuring the bowl is not touching the water. Allow to melt, stirring occasionally, then take off the heat and set aside.

Sift the flour, cocoa powder and a pinch of fine sea salt into a medium bowl. In a jug, lightly beat the eggs. Set both aside. Use electric beaters or a freestanding mixer to beat the butter and sugar for about 8 minutes until very pale and fluffy, scraping down the bowl every now and then. Continue mixing on a high speed while gradually adding the eggs, then stop beating and carefully fold in the flour mixture with a rubber spatula. Fold in the melted chocolate, soured cream and milk.

Divide evenly between the prepared cake tins. Use a rubber spatula to spread the mixture evenly, with a slight dip in the centre of each. Bake for about 35 minutes, making sure the tins are not touching; swap the cakes around after 20 minutes (not before), to ensure they cook evenly. To test that the cakes are ready, rather than using a skewer, press each one lightly with your finger – they should be firm and springy to the touch, and coming away from the side of the tin. Cool in the tins for 2 minutes, then carefully run a palette knife around the edge of each sponge; turn out onto a wire rack. Peel away the parchment and leave to cool completely.

Meanwhile, for the ganache buttercream, put the chopped chocolate in a bowl. In a small pan, heat the cream gently until steaming and starting to bubble at the edges; remove from the heat and pour over the chocolate. Allow to stand for 1 minute then stir until just combined (don’t overmix as it could become grainy); set aside to cool for 5 minutes. In another bowl, beat the butter and icing sugar until light and fluffy, then stir in the cooled chocolate mixture. Chill for 30 minutes until firm but spreadable.

To assemble the cake, put one sponge on a serving plate or cake stand. Use a palette knife to spread ½ the buttercream over it. Top with another sponge, spread over the remaining buttercream and finish with the final sponge. Chill for 30 minutes until firm.

For the icing, chop 90g chocolate and melt it with the golden syrup in a bowl over a pan of simmering water. Remove from the heat and sift over the icing sugar; stir it in, along with 2-3 tbsp hot water, until just combined. While still warm, pour the icing onto the top of the cake and use a palette knife to spread evenly. Use a peeler to create chocolate shavings with the remaining chocolate and scatter over the cake. Keep for up to 4 days in an airtight container.