Beat yolks and sugar in stand mixer on medium high for 12 minutes or until white and thick.
Add vanilla and mascarpone, beat until just combined. Transfer mixture to a bowl, set aside.
Beat egg whites until stiff.
Fold ⅓ of the yolk mixture into the egg whites. Then gradually fold the remaining yolk mixture in and mix until just combined. (It doesn't need to be perfectly smooth. It will look a bit "lumpy", being the egg whites, which means your cream mixture is lovely and light. The "lumps" smooth out when you spread the cream, and also while resting overnight.
Mix coffee and liquor together. Quickly dip biscuits in and line the bottom of a full sized gastro.
Spread over half the cream, then top with another layer of coffee dipped biscuits.
Spread with remaining cream.
Cover & refrigerate overnight
Dust with cocoa powder just before cutting & serving