Divide the egg yolks and the egg whites. Whisk the egg yolks with the sugar with a whisk or electric mixer until they become white and fluffy. Rub the egg cream between your fingers: when ready, it should be completely smooth.
Now add the mascarpone cheese and keep on whisking until it is completely combined. Add two tablespoons of vinsanto or of your favourite liqueur and stir in.
In a separate bowl whip the egg whites until stiff peaks form and gently fold them in.
In a large shallow dish spoon a few tablespoons of mascarpone cream and spread it evenly. Soak quickly the biscuits into the warm black coffee and make a layer of them over the mascarpone cream. Cover the ladyfingers with more mascarpone cream and sprinkle some chopped dark chocolate. Make two or three layers of biscuits and mascarpone cream, then finish with a generous dusting of cocoa powder. If you prefer, you can serve the tiramisu into individual cups.
Leave the tiramisu in the fridge for at least 2 hours before serving.