01 - Whisk egg yolks with powdered sugar in a heatproof bowl set over simmering water, stirring constantly for 2-3 minutes until mixture thickens and becomes pale yellow. Remove from heat and let cool for 5 minutes.
02 - In a chilled bowl, beat cold heavy cream using an electric mixer or whisk until stiff peaks form when beaters are lifted.
03 - Gently fold mascarpone cheese into cooled yolk mixture until completely smooth and no lumps remain. Fold whipped cream into mascarpone base in three additions until fully incorporated and uniform.
04 - Combine cooled espresso with coffee liqueur in a shallow baking dish wide enough to fit ladyfinger biscuits.
05 - Quickly dip ladyfingers into coffee mixture for 1-2 seconds per side—do not soak. Arrange half the dipped biscuits in a single layer in an 8-inch square baking dish, breaking to fit if necessary.
06 - Spread half the mascarpone cream evenly over ladyfingers using an offset spatula, reaching corners completely.
07 - Repeat dipping and arranging remaining ladyfingers over first cream layer. Top with remaining mascarpone mixture, smoothing surface completely.
08 - Cover tightly with plastic wrap and refrigerate for minimum 4 hours or overnight for optimal texture and flavor development.
09 - Just before serving, dust surface generously with cocoa powder using a fine-mesh sieve. Garnish with dark chocolate shavings if desired. Cut into squares and serve chilled.