01 - Whisk egg yolks and sugar in a heatproof bowl over gently simmering water until pale and thickened, about 3–4 minutes. Remove from heat and let cool slightly.
02 - Gently fold mascarpone cheese and vanilla into the cooled yolk mixture until smooth and creamy.
03 - In a separate bowl, whip cold heavy cream to stiff peaks. Carefully fold whipped cream into the mascarpone mixture until just combined.
04 - Combine espresso and coffee liqueur in a shallow dish for dipping ladyfingers.
05 - Quickly dip each ladyfinger into coffee mixture for 1–2 seconds per side. Arrange in a single layer in a 9 x 9 inch dish.
06 - Spread half of the mascarpone cream evenly over the ladyfingers.
07 - Add another layer of dipped ladyfingers. Top with remaining mascarpone cream and smooth the surface.
08 - Cover and refrigerate at least 4 hours, preferably overnight, to allow flavors to meld.
09 - Just before serving, dust generously with unsweetened cocoa powder and sprinkle with dark chocolate shavings if desired.