Put the chocolate in a large, heatproof mixing bowl. Pour the cream into a saucepan with the sugar and bring to a simmer over a medium heat, stirring continuously until the sugar is melted. Turn up the heat and bring to the boil, then quickly remove from the heat. Pour over the chocolate and whisk until smooth and glossy.

Use straight away or leave to cool until thick enough to spread on a cake. Alternatively, set aside to cool completely, then beat with an electric whisk until light and fluffy, and ready for spreading.