To garnish the martini glasses, dip the rim of the glasses in the egg white and then into a little cocoa powder to create a chocolate rim all around the edge of each glass.
Pour the vodka, cointreau, orange juice, cocoa powder and icing sugar in a cocktail shaker with plenty of ice.
Shake everything together for about 15 seconds.
Strain into the two martini glasses.
For a traditional martini finish, stick a cocktail stick through the chocolate eggs (as you would an olive) and sit in the glasses.