For 8 servings
Whisk egg yolks and sugar together until pale and thick, about 3 minutes. Fold in mascarpone until smooth.
Whip egg whites in a separate clean bowl until stiff peaks form.
Gently fold egg whites into mascarpone mixture in three additions until light and airy.
Mix coffee and liqueur in a shallow bowl. Dip ladyfingers briefly (about 1 second per side) β don't soak too long.
Arrange a layer of dipped ladyfingers in a 9Γ13 dish.
Spread half the mascarpone cream over the ladyfingers. Repeat layers.
Cover and refrigerate at least 4 hours, or overnight.
Dust generously with cocoa powder just before serving. Shave chocolate on top if desired.