In a small saucepan over medium-low heat combine semi-sweet chocolate, cocoa powder, sugar and ½ cup (4floz/115ml) milk, stirring until the chocolate is melted. Remove from the heat.

Stir the remaining 1 cup (8floz/225ml) of cold milk and the vanilla into the chocolate mixture. Set aside.

In a small bowl, whip the cream and the confectioner’s sugar (if using) until soft peaks form. Set aside.

Put the ice cubes in a blender, pour in the chocolate mixture and blend until smooth.

Pour into 4 glasses, top with a dollop of whipped cream and serve immediately with straws.