01 - Whisk egg yolks with powdered sugar in a heatproof bowl set over a pot of simmering water. Cook for 2-3 minutes, stirring constantly, until mixture thickens and becomes pale yellow. Remove from heat and allow to cool slightly.
02 - In a clean bowl, beat cold heavy cream using an electric mixer or whisk until stiff peaks form. Set aside.
03 - Gently fold mascarpone cheese into the cooled egg yolk mixture until smooth and fully incorporated. Carefully fold in the whipped cream until no white streaks remain.
04 - In a shallow dish, combine cooled brewed coffee with coffee liqueur. Stir to blend.
05 - Working quickly, dip each ladyfinger into the coffee mixture for 1-2 seconds per side. Arrange half of the dipped biscuits in a single layer in an 8-inch square dish.
06 - Spread half of the mascarpone mixture evenly over the ladyfingers using a spatula, ensuring complete coverage.
07 - Repeat with remaining dipped ladyfingers, followed by the rest of the mascarpone mixture. Smooth the top layer evenly.
08 - Cover dish tightly with plastic wrap. Refrigerate for at least 4 hours, or preferably overnight, to allow flavors to meld and texture to set.
09 - Just before serving, dust generously with unsweetened cocoa powder. Garnish with dark chocolate shavings if desired. Cut into squares and serve chilled.