Brew your espresso. Pour it into a shallow dish or bowl and add the Vin Santo, if using, and allow it to cool while you prepare the mascarpone cream.
Divide the egg yolks and the egg whites. With a whisk, an electric mixer or stand mixer, whisk the egg yolks with the sugar until they have turned pale yellow in color and are fluffy. The sugar granules should be completely dissolved. This should take a couple of minutes.
Add the mascarpone cheese and continue to mix until it’s completely combined.
In another bowl whip the egg whites until stiff peaks form.
Gently fold them into the mascarpone cream mixture, being sure not to deflate your egg whites.
In a large shallow casserole-style dish spoon out just a few tablespoons of the mascarpone cream and spread it evenly. This is important as it will keep the entire dessert from sticking to the bottom.
Quickly dunk the ladyfingers into the coffee (don’t let them sit in the coffee or they will fall apart - just a dunk on both sides will do) and layer them over the mascarpone cream, side by side, being careful not to overlap the cookies.
Cover the ladyfingers with about half the mascarpone cream.
Sprinkle a light layer of cocoa powder.
Make another layer of ladyfingers and the remaining cream in this fashion, finishing with a dusting of cocoa powder.
Refrigerate for at least 3 hours before serving, preferably longer.