01 - Whisk egg yolks and granulated sugar together in a heatproof bowl set over a pot of gently simmering water. Cook for 3-4 minutes until the mixture becomes pale and slightly thickened. Remove from heat and let cool slightly.
02 - Gently fold the mascarpone cheese and vanilla extract into the cooled yolk mixture until smooth and creamy.
03 - In a separate chilled bowl, whip the cold heavy cream until stiff peaks form. Carefully fold the whipped cream into the mascarpone mixture until just combined.
04 - Combine the cooled espresso and coffee liqueur in a shallow dish wide enough to dip 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 the bottom of a 9 x 9 inch baking dish.
06 - Spread half of the mascarpone cream evenly over the first layer of ladyfingers using a spatula.
07 - Add another layer of coffee-dipped ladyfingers over the cream. Top with the remaining mascarpone cream and smooth the surface evenly.
08 - Cover the dish with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow the flavors to meld and the dessert to set properly.
09 - Just before serving, dust the top generously with unsweetened cocoa powder using a sifter. Sprinkle with dark chocolate shavings if desired. Cut into squares and serve chilled.