Combine egg yolks and sugar in the top of a double boiler, over boiling water. Reduce heat to low, and cook for about 10 minutes, stirring constantly.
This is your sabayon, remove from the heat and whip yolks until thick and lemon colored. (whipping the eggs off the heat should allow them to cool off sufficiently if you're going to make a larger batch make sure to give the sabayon time to cool down before adding the rest of the ingredients.)
Add Mascarpone to whipped yolks, beat until combined.
In a separate bowl, whip cream to stiff peaks.
Gently fold the whipped cream in the mascarpone sabayon mixture and set aside.
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 an 8 inch square baking dish (or 6×9)
Spoon half the mascarpone cream filling over the ladyfingers.
Repeat process with another layer.
Refrigerate 4 hours or overnight.
Dust with cocoa before serving