Beat egg yolks with sugar until pale and thick, about 5 minutes.
Fold mascarpone into the yolk mixture with a spatula until smooth.
Whip egg whites to stiff peaks and gently fold into the cream in two additions.
Quickly dip ladyfingers in espresso and layer in a dish. Spread half the cream.
Repeat layers, cover and refrigerate at least 4 hours. Dust with cocoa before serving.