Sift the icing sugar.

Beat the egg.

Place the chocolate and butter in a bain marie/double boiler. As explained in my other recipes, at home this can be made using a pan with water and another smaller container, preferably metal, that can sit in the one with water.

Stir occasionally until the chocolate and butter melt. Add the egg and beat thoroughly.

The mixture should be thoroughly combined.

Remove from the bain marie and stir in the icing sugar then beat until smooth and glossy.

Pour on the cake for a smooth finish.

It.ca also be allowed to cool off for a piping with it.