In a bowl, whisk together the sugar and egg yolks. Gradually add the mascarpone and continue stirring until the mixture becomes creamy. In another bowl, whip the egg whites to a meringue consistency (stiff peaks). Carefully fold the meringue into the mascarpone mixture. Quickly and lightly dip enough ladyfingers or biscuits into the brewed espresso to line the bottom of an 8-by-8-inch pan or glass serving dish. Cover the ladyfingers or biscuits with one half of the mascarpone mixture, followed by a thorough dusting of cocoa and shaving of chocolate. Repeat the layering process. Once assembled, shake the pan lightly to settle the ingredients. Chill at least two hours (overnight is preferable) before serving. Cut into portions and serve.