01 - Whisk egg yolks with powdered sugar in a heatproof bowl set over a pot of simmering water for 2-3 minutes until thick and pale. Remove from heat and allow to cool slightly.
02 - Beat cold heavy cream in a separate bowl until stiff peaks form. Set aside until needed.
03 - Gently fold mascarpone into cooled egg mixture until smooth and incorporated. Carefully fold whipped cream into mascarpone mixture until fully combined and uniform.
04 - Combine cooled coffee with coffee liqueur in a shallow dish. Stir gently to blend flavors.
05 - Quickly dip each ladyfinger into coffee mixture for 1-2 seconds per side. Biscuits should be moistened but not saturated or falling apart.
06 - Arrange half of dipped ladyfingers in single layer in 8-inch square dish. Spread half of mascarpone mixture evenly over biscuits.
07 - Repeat with remaining dipped ladyfingers, followed by remaining mascarpone mixture. Smooth top layer with spatula.
08 - Cover tightly with plastic wrap. Refrigerate for minimum 4 hours or overnight for optimal texture and flavor development.
09 - Generously dust surface with cocoa powder before serving. Garnish with dark chocolate shavings if desired. Cut into squares and serve chilled.