Place the castor sugar and water in a pan over medium-low heat. Stir until the sugar dissolves and then add the orange peel. Simmer for 2 minutes until slightly thickened. Remove the orange peel and add the chocolate. Stir until melted, then whisk in the cream, cocoa and 1/3 C (80 ml) milk. Transfer to a jug and keep to one side.

Meanwhile, warm the remaining milk in a pan over medium-low heat to just below boiling point. Divide among mugs and add the warm chocolate mixture to taste. Stir, top with whipped cream, add a dusting of cocoa powder and serve.