Dip 12 ladyfingers quickly in espresso. Arrange in a row in a shallow platter. Beat egg yolks with sugar until pale. Add mascarpone and rum or brandy and mix well. Beat egg whites until stiff but not dry; fold into mascarpone mixture. Spread half of mascarpone mixture over ladyfingers. Sprinkle with half of chocolate. Dip remaining ladyfingers in remaining espresso. Spread with remainder of mascarpone mixture. Sprinkle with remaining chocolate. Cover lightly with foil. Refrigerate.
