125g castor sugar
100g self-raising flour
25g cocoa powder
40g unsalted butter melted
1 teaspoon vanilla extract
375g dark cooking chocolate such as Nestlė Premium Dark,
broken into small pieces.
(Supermarket brands mostly consist of milk solids and almost no cocoa).
250g unsalted butter
100g icing sugar sifted
Put the sugar and eggs into heat proof bowl set over a saucepan of gently simmering water.
Whisk, using electric whisk, for 5-10 minutes until whisk leaves a trail when lifted above the mixture.
Sift over the flour and cocoa powder and carefully fold into the mixture with the melted butter and vanilla extract until combined. Pour this mixture into a greased and lined 20cm spring-form cake tin and bake in pre-heated oven, 180°C for 25 minutes. After 5 minutes turn out onto cooling rack. Once cold slice in half horizontally.
Melt the chocolate and butter together in a heat proof bowl set over a saucepan of gently simmering water. Remove from the heat and beat in the icing sugar. Set aside to cool and then chill for 1 hour until thickened. Then beat until pale and fluffy.
Use half of the icing to sandwich the two halves of the cake together. Use the remaining icing to cover the top and sides of the cake, swirling the icing with a palette knife. Decorate with curls of white chocolate.