This devilishly delightful chocolate cake is made with fluffy interior and sumptuous chocolate fudge frosting. Seriously decadent!
Makes one 4-layer chocolate fudge cake.The cake will keep in the fridge for up to 3 days.
For the cake, preheat the oven to 350 ºF (180 ºC). Grease four 8-inch (20 cm) cake pans, dust with flour, tapping out any excess and line the bottom of each pan with parchment paper.
Sift the flour, cocoa, granulated sugar, baking powder, baking soda and salt into a large mixing bowl using electric beaters or into the bowl of a stand mixer fitted with the paddle attachment. Stir in the brown sugar.
In a separate bowl, whisk together the buttermilk, oil, coffee, eggs and vanilla. Add this all at once to the dry mixture and mix first on low speed (using electric beaters, if not using a stand mixer) until blended, then increase the speed to medium and beat for a minute until smooth (the batter will be fluid). Pour this into the prepared pans and bake for about 30 minutes, until a tester inserted in the centre of the cake comes out clean. Cool the cakes in the pans for 30 minutes, then turn out to cool completely.
For the frosting, melt the butter and chocolate in a metal bowl placed over an inch (25 mm) of barely simmering water, stirring until melted. Set this aside to a cool a little, but it should still be a lukewarm to use.
Using electric beaters or in a stand mixer fitted with the paddle attachment, beat the melted chocolate & butter with the cocoa powder and half of the icing sugar on medium speed until smooth. Add the sour cream, vanilla and salt and beat in. Add the remaining icing sugar and beat on medium speed until smooth and a spreadable consistency. If the frosting seems too soft at this point, just let it sit for a bit, then beat again, but avoid increasing the speed any higher than medium – this will make the frosting fluffy and light, but no longer fudgy.
Place a cake layer (parchment peeled off) on a cake plate. Dollop frosting onto this and spread to the edges in a level layer. Top this with a second cake layer and repeat with the frosting and remaining two cake layers. Use the remaining frosting to cover the top and sides of the cake. Chill the cake until ready to serve.