(Makes 12-14 slices)250g light soft brown sugar
75g spreadable butter
2 medium eggs, lightly beaten
175g plain flour
75g dark chocolate drops
1tsp bicarbonate of soda
For the butter icing:
50g spreadable butter
100g icing sugar, sieved
For the chocolate frosting:
125g dark chocolate chips
300g icing sugar, sieved
1-2 tbsp hot water
1 large egg yolk, lightly beaten
50g butter, melted
Pre-heat the oven to 175C/160C fan. Prepare two 8-inch sandwich tins.
Cream the butter and sugar together and beat well. This will have a strange texture – not pale and fluffy like usual creaming – because of the high proportion of sugar to butter.
Add the egg, little by little, beating well all the time. Stir in the flour, very gently, bit by bit (or use the pulse setting on the mixer, and add the flour through the feed tube in spoonfuls). Stir the bicarbonate into the milk, then add it to the cake mix, stirring all the time.
Melt the chocolate in a bowl over hot water or in the microwave (this takes about two to two-and-a-half minutes on full power). Let it cool a little, then stir gently into the cake mix.
Turn the mix into the sandwich tins, dividing it evenly, and smooth the tops. Bake for 30-35 minutes, or until the cakes are springy or a knife inserted in the centre comes out clean.
Allow to cool for a couple of minutes in the tins, then turn out on to a rack to cool completely.
To make the butter icing, put the 50g of butter and 100g of sieved icing sugar into a mixing bowl and beat together. Add a few drops of warm water to soften it if necessary, and keep beating until the mixture gets really light and fluffy.
To make the chocolate frosting, melt the 125g of chocolate in a bowl over hot water, or in the microwave. Stir in the 300g of icing sugar with a little hot water. This will be tricky and the texture will become very granular, but keep going until it's nearly mixed in, then, using an electric mixer if possible, gradually beat in the egg yolk and butter, adding a little more hot water as necessary, to reach a smooth, spreadable consistency.
Sandwich the cakes together with butter icing, then spread the entire cake with chocolate frosting.