(click on the text to highlight each stage):
- Preheat the oven to 180°C/fan160°C/gas 4. Grease a 20cm round, deep cake tin and line with baking paper. Place the 125g of plain chocolate with 50g of the butter in a bowl and melt over a pan of hot water. Remove from the heat and stir in the remaining butter.
- Mix the milk and vinegar. Place all the other cake ingredients in a large mixing bowl. Pour in the milk mixture and chocolate butter mixture. Beat until smooth. Spread into the cake tin and bake for 1 hour, until firm in the centre. Cool for 10 minutes, then turn out and cool completely.
- Meanwhile, make the icing. Melt the 225g of plain broken up chocolate and butter together in the microwave for 3 minutes on medium, stirring halfway through. Alternatively, melt the chocolate and butter in a bowl over a pan of just simmering water. Stir until smooth, then beat in the cream. Cool slightly
- Halve the cake through the middle. Spread a quarter of the icing on 1 half and sandwich together. Spread the rest over the top and sides and decorate with chocolate curls, silver balls, chocolate buttons or whatever takes your fancy!