(from: Bea Vo - Tea with Bea)
225g dark chocolate (I used 125g 69% and 100g 78%), broken into pea-sized pieces
65g cocoa powder
1/2 teaspoon baking soda
1/4 teaspoon salt
For the glaze:
125 dark chocolate, grated or broken into small pieces
Preheat the oven to 170°C. Line a 24cm diameter springform pan with parchment paper and grease with butter. (Bea suggest that you can also bake it in two 18cm diameter springform pans.)
Put the chocolate and cocoa powder in a large, heatproof bowl. Melt the butter in a sauce-pan over medium heat. When it has melted, pour over the chocolate and cocoa and stir until this is all melted and smooth.
In another bowl, whisk together eggs and sugar. Pour this into the chocolate mixture and mix until well combined.
Put the flour, baking soda and salt in a large mixing bowl, sift twice. Add one third of the flour mixture to the chocolate mixture and mix until well incorporated. Add half the buttermilk and mix until just combined. Repeat with another third of the flour and the other half of the buttermilk. Finally, add the last third of flour mixture and mix until thorougly combined.
Pour the mixture into your prepared springform pan. Bake for about 35-40 minutes. A skewer inserted into the middle of the cake should come out clean. Mine was still pretty soft in the middle after 45 minutes, but I took it out of the oven anyway to prevent it from turning black in the surface. It sunk in the middle after cooling down.
For the glaze: Bring 125ml cream to the boil in a small saucepan. Remove from the heat, stir in chocolate and whisk until it has melted and the mixture is smooth. Spread over your cake and decorate.