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 extract into the cooled yolk mixture until smooth and creamy.
03 - In a separate bowl, whip cold heavy cream to stiff peaks using an electric mixer or hand whisk.
04 - Carefully fold the whipped cream into the mascarpone mixture until just combined. Avoid overmixing to maintain light texture.
05 - Combine cooled espresso and coffee liqueur in a shallow dish for dipping ladyfingers.
06 - Quickly dip each ladyfinger into the coffee mixture for 1-2 seconds per side. Do not soak—ladyfingers should remain firm.
07 - Arrange dipped ladyfingers in a single layer in a 9 x 9 inch dish. Spread half the mascarpone cream evenly over the ladyfingers.
08 - Add another layer of dipped ladyfingers. Top with remaining mascarpone cream and smooth the surface with a spatula.
09 - Cover and refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld and set properly.
10 - Just before serving, dust generously with unsweetened cocoa powder using a sifter. Sprinkle with dark chocolate shavings if desired.