Place milk and vanilla bean into a 2 quart saucepan, bring to a boil, remove from heat and add espresso. In a mixing bowl beat the eggs to golden and gradually add sugar until light yellow ribbons have formed. Place back into milk pan and cook slowly until mixture coats back of spoon thickly and sets slightly to custard. Texture should resemble thick gravy. DO NOT BOIL OR MIXTURE WILL CURDLE. Remove vanilla bean and cool in refrigerator for 1/2 hour.
Whip cream to stiff peaks and fold into custard mixture. Place mixture into ice cream machine and freeze according to manufacturers instructions. Remove and freeze 2 hours. Place 1 scoop coffee ice cream into each of 4 water glasses. Pour 1 cup of cooled coffee over each scoop, dollop with remaining whipped cream and dust with bitter cocoa.