Combine egg yolks and sugar in a medium-sized bowl and beat well. In a separate bowl, beat the egg whites to stiff peaks. In a third, larger bowl, combine the egg yolk mixture with the mascarpone, then fold in the egg whites to produce a creamy mixture.
Arrange a tight layer of ladyfingers in a 9-by-12-inch serving dish. Using a spoon, drizzle about half the liqueur and half the espresso over the ladyfingers. Cover the ladyfingers with the mascarpone mixture and the grated chocolate, and dust it with a little more than half the cocoa. Cover the filling with a second layer of ladyfingers and drizzle with the remaining liqueur and espresso. Place the dish in the refrigerator for at least 12 hours (the tiramisu can be made 24 hours in advance). Top with the remaining cocoa before serving.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.
Recipe courtesy of "Sophia Loren's Recipes and Memories" by Sophia Loren, GT Publishing