Method

1. Preheat the oven to 180°C (350°F), Gas mark 4. Butter and flour the sides of the sandwich tins (two 20cm (8in) diameter sandwich tins) and line the bases with greaseproof paper.
2. Place the chocolate and the milk in a bowl sitting over a saucepan of gently simmering water and heat until then chocolate has melted.
3. Beat the butter until very soft then add the caster sugar and continue to beat until the mixture is light and fluffy. Beat in the eggs, one at a time, then fold in the melted chocolate.
4. Sift in the flour, cocoa powder, baking powder and the bicarbonate of soda, and fold in gently to mix. Divide the mixture between the two tins and bake in the oven for about 25 minutes, or until a skewer inserted into the middle of each cake comes out clean.
5. Remove the cakes from the oven and allow to sit for a few minutes before turning them out of their tins and placing them on a wire rack to cool.
6. While the cakes are cooling, make the chocolate butter icing. Beat the butter, cream and the vanilla extract until very soft. Then gradually sift in the icing sugar and the cocoa powder, beating all the time, until it is all added. Continue to beat until very soft, then whisk the mixture until it is light and fluffy. (I normally make the chocolate butter icing in an electric food mixer, using the whisk all the way through.)
7. Once the cakes are cool, sandwich them together (I normally sandwich them together bottom to bottom – if you know what I mean!) with the chocolate butter icing. Place the cake on a plate or a cake stand and dust with cocoa powder or icing sugar if you wish.