01 - Whisk egg yolks and sugar together in a heatproof mixing bowl over a pot of gently simmering water (bain-marie) until pale and slightly thickened, approximately 3-4 minutes. Remove from heat and allow to cool slightly.
02 - Gently fold mascarpone cheese and vanilla extract into the cooled yolk mixture until smooth and creamy consistency is achieved.
03 - In a separate chilled bowl, whip heavy cream to stiff peaks using electric mixer or hand whisk. Carefully fold whipped cream into mascarpone mixture until just combined.
04 - Combine cooled espresso and coffee liqueur in a shallow dish suitable for dipping ladyfingers.
05 - Quickly dip each ladyfinger into coffee mixture for 1-2 seconds per side; do not soak. Arrange single layer of dipped ladyfingers in 9 x 9 inch baking dish.
06 - Spread half of mascarpone cream evenly over ladyfinger layer using spatula.
07 - Add another layer of coffee-dipped ladyfingers. Top with remaining mascarpone cream and smooth surface evenly.
08 - Cover dish with plastic wrap or lid. Refrigerate at least 4 hours, preferably overnight, to allow flavors to meld and texture to set properly.
09 - Just before serving, dust generously with unsweetened cocoa powder using sifter. Sprinkle with dark chocolate shavings if desired. Slice and serve chilled.