Add the beaten whites. You're going to get a light cream. Dip each biscotti for 5 sec. in the coffee with amaretto. Arrange half the biscotti in a glass container to cover the bottom.
Pack the biscotti tightly next to each other along the walls of the container. Place half the cream on top and smooth it out. Arrange the 2nd layer of biscotti perpendicular to the 1st.
Smear with the rest of the cream and sprinkle generously with powdered cocoa. Leave it in the fridge for 8 hours. Before serving, sprinkle with grated chocolate.