Whisk egg yolks and sugar in a bowl over a pot of simmering water until thick and creamy.
- Remove from heat and cool slightly, then mix in the mascarpone cheese.
- Dip ladyfingers briefly in the espresso and layer them in a dish.
- Spread half of the mascarpone mixture over the ladyfingers.
- Repeat with another layer of espresso-dipped ladyfingers and mascarpone mixture.
- Chill in the refrigerator for at least 4 hours.
- Dust with cocoa powder before serving.