01 - Whisk egg yolks and sugar together in a heatproof bowl set over a pot of gently simmering water. Beat 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.
03 - In a separate chilled bowl, whip heavy cream until stiff peaks form. Carefully fold whipped cream into the 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 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.
06 - Spread half of the mascarpone cream evenly over the ladyfinger layer using a spatula.
07 - Add another layer of dipped ladyfingers. Top with remaining mascarpone cream and smooth the surface evenly. Cover and refrigerate for at least 4 hours, preferably overnight, to set completely.
08 - Just before serving, dust generously with unsweetened cocoa powder using a sifter. Sprinkle with dark chocolate shavings if desired.