Combine egg yolks and sugar in the top of a double boiler, over boiling water using a whisk to mix. Reduce heat to low, and cook for about 10 minutes, stirring constantly with a wire whisk. This is your sabayon, remove from the heat and continue to whip yolks until thick and lemon-colored. Allow to cool briefly before mixing in mascarpone.
Add room temperature Mascarpone to whipped yolks, mix until well combined.
In a separate bowl, using an electric mixer whip cream to stiff peaks. (hand mixer or stand mixer is fine)
Gently fold the whipped cream in the mascarpone sabayon mixture and set aside. The mascarpone does not have to be at room temperature, but it will help it mix in easier if it is. Take it out of the refrigerator as you gather ingredients to make the recipe.
Mix the cold espresso with the coffee liquor and dip the ladyfingers into the mixture just long enough to get them wet, do not soak them!
Arrange the ladyfingers in the bottom of a 9-inch square baking dish (or container similarly sized)
Spoon half the mascarpone cream filling over the ladyfingers.
Repeat process with another layer of ladyfingers
Add another layer of tiramisu cream
Refrigerate at least 4 hours. Overnight is best.
Dust with cocoa before serving