Step 1

Heat the oven to 180C/fan 160C/gas Line 2 x deep 20cm springform cake tins with baking paper. Stir together the flour and cocoa in a bowl. Melt the chocolate, sugar and butter with 100ml water in a pan until smooth, then leave to cool.

Step 2

Once cooled, transfer to a mixing bowl and whisk in the eggs one by one until combined, followed by the vanilla extract. Slowly whisk the wet ingredients into the dry ingredients and stir until fully combined.

Step 3

Divide the batter between the cake tins and bake for 30 minutes or until a skewer poked into the middles comes out clean. It may crack a little on top but this will be covered by the icing. Leave to cool.

Step 4

To make the buttercream, use electric beaters to whisk together the icing sugar and butter for 5 minutes or until light and fluffy. Mix in the melted chocolate until smooth and the buttercream becomes spreadable. Put a thick layer of buttercream on top of one of the cakes, then sandwich the other sponge on top. Spread another thick layer on top, then use the rest to cover the sides. Leave to set in the fridge for 20 minutes.

Step 5

To make the topping, use a large knife or peeler to scrape across the surface of the chocolate to create curls and shards. Use these to top the cake along with a light dusting of cocoa powder.