125g unsalted butter, chopped
150g dark cooking chocolate, chopped
1 1⁄4 cups caster sugar
1⁄3 cup water
1⁄2 cup cocoa powder
3 eggs, lightly beaten
1 1⁄2 cups self-raising flour 1 cup buttermilk
200g unsalted butter, chopped, at room temperature
1 1⁄3 cups icing sugar mixture
200g dark cooking chocolate, melted, cooled
Grease a 22cm round cake pan. Line base and side with baking paper.
Combine butter, chocolate, sugar and water in a large saucepan over a low heat. Stir until butter and chocolate are melted and sugar is dissolved. Transfer to a large bowl. Whisk in sifted cocoa until smooth. Stand for 10 minutes.
Whisk eggs into chocolate mixture. Add flour and buttermilk, in two batches, whisking until combined. Pour into prepared pan.
Cook in a moderately slow oven (160C) for about 1 hour, or until a skewer inserted into the centre comes out clean. Remove. Stand in pan for 15 minutes. Transfer to a wire rack to cool.
To make icing, beat butter in a small bowl of an electric mixer until pale. Add sugar, 1⁄2 cup at a time, beating until smooth. Add chocolate. Beat until combined.
Cut cake in half horizontally. Sandwich cakes together with half the frosting (about 11⁄4 cups). Spread remaining frosting over the top.
Cut into wedges to serve.