01 - Whisk egg yolks and sugar in a heatproof bowl over a pot of gently simmering water until pale and slightly 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 the coffee mixture for 1-2 seconds per side. Arrange a single layer of soaked ladyfingers in a 9 x 9 inch dish. Spread half of the mascarpone cream evenly over the ladyfingers.
06 - Add another layer of dipped ladyfingers. Top with the remaining mascarpone cream and smooth the surface evenly.
07 - Cover and refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld and texture to set.
08 - Just before serving, dust generously with unsweetened cocoa powder and sprinkle with dark chocolate shavings if desired.