1) Chop the chocolate into small pieces and melt in a small heavy saucepan or in the top of a double boiler over simmering water. Stir occasionally until melted. Add the hot chocolate mix and sugar, stirring constantly until blended.
2) Remove from heat and slowly add 225ml of the milk, stirring until smooth. Cool to room temperature.
3) In a blender, place the remaining 250ml of milk, the chocolate mixture, and the ice. Blend on high speed until smooth and the consistency of a frozen daiquiri. Pour into a giant goblet and top with whipped cram and chocolate shavings.