Cut the chocolate in small squares pieces and put them in a pot. Add the milk and heat until chocolate is melted. The mixture should be fairly thick. Stir it well and let the mixture cool. Separate the egg white from yolks. In a large bowl beat together egg whites and the sugar until stiff. In another bowl, beat the heavy cream until it becomes frothy. Put the egg yolks in the cooled chocolate mixture and mix it. Add the beaten egg white and whipped heavy cream into the chocolate mixture and mix well. Pour the mousse au chocolat in the serving bowls and garnish with chocolate shavings. Chill at least 2 hours before serving and then serve.