In a medium heavy saucepan, scald the cream over medium heat until small bubbles form at the edges. Add the coffee and stir with a whisk to dissolve. Add the chocolate and stir occasionally for about 1 minute. Remove from the heat and transfer the mixture to a bowl to stop it from cooking any further. Let the icing stand for about 15 minutes, stirring every now and then, until it’s room temperature and has slightly thickened.