Take the mascarpone out of the fridge and brew 2 cups of strong coffee.
Separate the eggs and add 4 tablespoons of sugar to the yolks, saving the other 2 for the whites.
Whip the egg yolks and sugar until they turn pale in color. Add the mascarpone cheese gradually and mix well. Set aside.
Add the vanilla and the Marsala wine, rum or rum extract to the coffee (if using) and dip the ladyfingers in the coffee mixture for one second per side. Place them in your 9-inch by 13-inch pan one by one until you've lined the bottom.
Clean your beaters well and start whipping your egg whites with the cream of tartar. When they reach soft peaks add the remaining 2 tablespoons of sugar, one at a time.
Gently fold the mascarpone mixture into the egg whites with a spatula.
Smooth half of the mascarpone and egg white mixture over the bottom layer of coffee-soaked ladyfingers and dust the top of the mascarpone layer with cocoa powder. Finely grate some dark chocolate on top as well.
Add another layer of coffee-soaked ladyfingers over the cocoa-dusted mascarpone layer and then top with the remaining mascarpone mixture, smoothing it out as much as possible.
Cover with plastic wrap and refrigerate for 2 hours or overnight.
Dust with the remaining cocoa powder and grate some dark chocolate right before slicing and serving.