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