• Pre-heat oven to 180°C /160°C fan assisted / gas mark 4 / 350°F and line and grease 2 x 8 inch (20cm) round (4 inch (10cm) deep) cake tins.
• Melt the chocolate in a bowl set over a saucepan of simmering water or in the microwave then set aside.
• In a large mixing bowl whisk together the flours, cocoa powder, espresso powder, bicarbonate of soda and salt until well mixed.
• In a separate bowl mix together the buttermilk, sugars, olive oil, eggs and vanilla then beat into the flour mixture.
• Finally mix in the melted chocolate until completely incorporated.
• Divide the mixture between the 2 cake tins and bake in the oven for 30 minutes.
• Turn out the cakes and cool on wire racks before filling with buttercream.

Salted Caramel

• To make the Salted Caramel pour the caster sugar into a small saucepan into an even layer and heat on a medium temperature until the sugar melts. Do not stir the sugar but make sure it melts evenly by swirling the saucepan every so often.
• Once melted, carefully add in the double cream and butter, the caramel will bubble up vigorously. At this point you can stir the bubbly mixture until the caramel is smooth.  Remove from the heat then stir in the vanilla and salt.
• Chill the caramel overnight where it will set and thicken.
• Use half of the cold caramel (250g) in the buttercream, reserving the rest (250g) for drizzling over the cake.

Salted Caramel Swiss Meringue Buttercream

• To make the Salted Caramel Swiss Meringue Buttercream
• Heat the egg whites, caster sugar and light soft brown sugar in a bain marie, stirring constantly until the sugar has dissolved and the temperature has reached 160°F (71°C).
• Remove the egg whites and sugar from the heat and pour into a stand mixer with whisk attachment. Whisk until the mixture hast hickened and stiffened and has cooled to room temperature. About 68°F to 75°F (20°C to 24°C).
• Change the attachment to a paddle attachment. On a low speed add the butter slowly cube by cube. When you have almost added all the butter the mixture will look curdled. Do not fret – this is supposed to happen and just means you are nearly done. Just continue to add all the butter. Once the butter is totally incorporated the buttercream will miraculously become a smooth velvety consistency.
• Add the salt, vanilla extract and half of the chilled salted caramel. Mix until thoroughly combined.

Assembly

• Place one of the cake sponges on a cake board then spread a thick and even layer buttercream over the top. Place the second chocolate sponge cake on top.
• Cover the cakes with a thin layer of buttercream as a crumb coat. This will ensure the first layer of buttercream catches all the loose crumbs of the cake. Place the cake in the fridge for an hour for the crumb coat to firm up.
• Once the crumb coat is firm then cover the cake with the rest of the buttercream. Place back in the fridge for an hour for the second coat of buttercream to firm up which will help form a solid base for the caramel drizzle.
• Pour the reserved caramel in a saucepan and turn the heat on for about 5 seconds. The edges of the caramel will just start to melt. Immediately remove from the heat and stir the caramel. It should be a just about pourable consistency.
• Pour the caramel all over the top of the cake, starting at the centre and working out, encouraging some of the caramel to drip over the side.
• Serve the cake at room temperature.