Reduce speed to low. Add cocoa mixture in 2 batches, alternating with the buttermilk. Divide batter evenly between pans. Bake until a cake tester inserted into centre comes out clean, about 35 ...
Line a 10 inch cake tin with parchment paper. Place the sugar, chocolate, butter and water in a saucepan and cook gently until the chocolate and butter have melted. Cool Whisk in the buttermilk ...
Allow to cool until lukewarm. Add the butter and beat with an electric whisk for 5 minutes. Beat in the icing sugar and then the buttermilk. Place in a piping bag and pipe onto cake.
In a large bowl, whisk together flour, baking soda and a pinch of salt. Add buttermilk and eggs and whisk until just combined. In a small bowl, mash raspberries with a fork and set aside.