Combine the egg yolks, granulated sugar, and salt in a large heat-proof bowl.

Set it over a saucepan filled with simmering water. Whisk constantly until the mixture thickens and becomes pale, reaching a temperature of 165°F-170°F.

Allow it to cool for 5-10 minutes.

Whisk the cold mascarpone and vanilla extract into the cooled egg mixture. Stir until fully combined and smooth.

In a separate bowl, beat the cold heavy whipping cream to medium-stiff peaks.

Gently fold half of it into the mascarpone mixture, then incorporate the remaining half.

In a shallow dish, mix the cold espresso and optional Kahlua.

Quickly dip each ladyfinger into the mixture to soak them without becoming mushy.

Layer half of the soaked ladyfingers in the bottom of a 9x13-inch baking pan.

Spread half of the mascarpone mixture over the ladyfingers in the pan.

Repeat with another layer of dipped ladyfingers and cover them with the remaining mascarpone mixture.

Dust the top generously with unsweetened cocoa powder.

Cover the dish with plastic wrap and refrigerate for at least 8 hours or overnight before serving to fully set and develop flavors.