Melt the dark chocolate in a water bath. Put the chocolate in a piping bag and cut off a small corner. In 4 glasses (approx. 1/4 litre capacity), squirt a pattern with the chocolate onto the inner glass wall. Finely chop the white chocolate.
Heat the milk and melt the chocolate in it. Whip cream and vanilla sugar until half stiff. Pour the chocolate milk into the glasses. Spread the cream on top and serve dusted with gingerbread spices