1. 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. Allow to cool briefly before mixing in mascarpone.
2. Add mascarpone to whipped yolks, beat until combined.
3. In a separate bowl, whip cream to stiff peaks.
4. 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.
5. Mix the cold espresso with the coffee liquor and dip the lady fingers into the mixture just long enough to get them wet. Do not soak them!!
6. Arrange the lady fingers in the bottom of a 9 inch square baking dish (or container similarly sized).
7. Spoon half the mascarpone cream filling over the lady fingers.
8. Repeat process with another layer of lady fingers.
9. Add another layer of tiramisu cream.
10. Refrigerate 4 hours or overnight.
11. Dust with cocoa before serving.