This indulgent cake combines two of my favourite flavours: rich, fudgy chocolate and salted caramel. I’m always asked to make it for family birthdays – it’s a proper celebration piece, a showstopper to be met with guaranteed ‘oohs’ and ‘aahs’.
Preheat the oven to 180°C/fan 160°C/ gas 4. Make the sponge. Whisk the cocoa powder, light brown soft sugar, vanilla paste and water in a mixing bowl until smooth. Leave to cool for 5 minutes. Sift together the flour, baking powder and bicarbonate of soda in a separate bowl.
Beat the butter and caster sugar in a stand mixer fitted with the beater, on medium speed for 3-5 minutes, until pale and creamy, scraping down the sides of the bowl from time to time. Beat in the eggs, one at a time, mixing in 1tbsp of the flour mixture after each egg.
Fold in the remaining flour mixture, a third at a time, until well incorporated, then fold in the cooled cocoa mixture.
Divide the sponge mixture equally between the lined tins and level with a palette knife. Bake on the middle shelf for 20-25 minutes, until risen and a skewer inserted into the centres comes out clean. Remove from the oven, leave to cool for 5 minutes, then turn out onto wire racks to cool completely.
Meanwhile, make the salted caramel. Put the caster sugar and 6tbsp of water in a saucepan over a medium heat. Cook for 6-8 minutes, without stirring, until the caramel starts to turn deep amber. Remove from the heat and place the pan in a bowl of cold water to stop the cooking process. Slowly whisk the cream and vanilla extract into the caramel until you have a thick pouring consistency (if necessary, return the pan to a low heat, stirring continuously, to reduce a little). Stir in the sea salt and leave to cool.
Make the buttercream. Whisk the egg whites and sugar together in a heatproof bowl until smooth. Next set the bowl over a pan of simmering water and heat for 5 minutes, whisking occasionally, until the sugar dissolves – the mixture should feel smooth, not grainy, between your fingertips.
Pour the egg white mixture into the bowl of a stand mixer fitted with the whisk and mix for about 7 minutes, to stiff peaks. Add the butter, then whisk for about 5 minutes, until smooth and glossy. Don’t panic if the mixture appears to curdle or turn lumpy – keep whisking until it becomes smooth. Add the vanilla extract and, a tablespoon at a time, add 5tbsp of the cooled caramel, and then mix until smooth.
Level the cakes if necessary and divide the buttercream between 3 bowls. Secure one of the sponges to the cake board using a little bit of buttercream.
Using the buttercream from one of the bowls, spread it over the top of the sponge on the cake board, and on top of two other sponges, stacking them on top of one another. Top the cake with the remaining fourth sponge. Using the buttercream from the second bowl, carefully spread it over the outside of the cake with a palette knife. For the semi-naked look, run a cake scraper around the outside of the cake with a firm pressure, so that parts of the cake appear through the buttercream.
Chill for 30 minutes. Remove the cake from the fridge and pour the cooled salted caramel into the paper piping bag, twist the top to seal and snip the end. Pipe around and over the edge of the cake to create drips running down the side. Spread the remainder of the caramel over the top of the cake. Spoon the final third bowl of buttercream into the piping bag fitted with the nozzle and pipe around the top of the cake. Do not pipe too close to the edge, as the buttercream can slide off. Decorate with caramel chocolates, popcorn or honeycomb.