Start this recipe by making the tiramisu cream. Put the egg yolks and sugar in a bowl and mix together with an electric beater till thick and glossy (it should take about 5 minutes). In another bowl, whip the egg whites to stiff peaks. Gently fold the tiramisu mascarpone into the egg yolk and sugar mixture. Finally, fold in the whipped egg whites and mix well to obtain a rich, light cream. You can now begin to put the dessert together. Mix the alcohol with the cold coffee. Dip the sponge finger halves into the coffee mixture and arrange in the bottom of the each glass (2 or 3 pieces in each glass). Pour over a tablespoon of the coffee mixture into each glass and then equally spoon over ½ of the tiramisu cream. In each glass, add a spoonful of the chopped chocolate. Sift over some cocoa powder, and repeat the whole process again, creating a second layer of each filling. You should end up with a layer of chocolate pieces on top. Finally, sift the remaining cocoa powder on top and place the tiramisu glasses in the fridge to chill and set for 2 hours before serving, or overnight.