1 Into a basin fitted over a pan of barely simmering water, break the chocolate.
2 Add in the soured cream and stir.
3 Keep the heat low until the chocolate has melted.
4 Remove the pan from the heat.
5 Allow the mixture to cool.
6 Use to spread over the centre and top of a chocolate sponge.
7 Decorate with a few walnuts or hazelnuts.