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 the entire time. After 10 minutes over the double boiler, remove from the heat and whip yolks until thick and yellow.
Allow to cool
Now add your Mascarpone to your whipped yolks and beat until it is well combined.
In a separate bowl, using an electric mixer whip your cream until it starts to form stiff peaks.
Next, fold the whipped cream in the mascarpone sabayon mixture and then set aside.
Now, mix your espresso with the coffee liquor or other liquor if you are using it in a large coffee mug that will cover the ladyfingers completely when you dip them vertically in the cup. This is important since you want to quickly dip the lady fingers and then get them out of the espresso.
So now, quickly dip each lady finger into your mug vertically and then place in a 8x8 pan. You do not want to have the ladyfinger feel too wet because it actually keeps absorbing liquid after you take it out and after assembling your tiramisu. Continue doing this until your lady fingers are nicely arranged in one tight layer in your pan making sure not to overlap them.
Now, add your sabayon mixture (egg yolks, cream and mascarpone) gently over top of the first layer of ladyfingers. Try to make the layer about 3/4 inch thick.
After this layer, you're going to add another layer of ladyfingers dipped in your espresso mixture like above.
After adding your second layer of ladyfingers, add the final layer of sabayon mixture, again about 3/4 inches thick. You may have some leftover which you can use to go with fresh fruit later!
Dust the entire top layer of sabayon lightly with some cocoa powder.
Cover with plastic wrap and let sit in the fridge for at least 6 hours but preferably over night.