Whisk three of the egg whites until stiff, then set aside.
Whisk the egg yolks with the sugar until pale and voluminous, then whisk in the mascarpone, a little at a time, until smooth and well combined.
Gently fold the mascarpone minute into the three whites a little at a time with a large metal spoon, being careful to knock as little air out as possible.
Stir the booze into the coffee and pour into a shallow dish.
Briefly dip each biscuit into the liquid until it is a pale coffee colour, then arrange to cover the base of a shallow glass dish.
Spoon a third of the mascarpone mixture on top, followed by a good sprinkle of cocoa, then repeat the layers, finishing with a layer of the cheese and cocoa.
Cover and refrigerate for six hours before serving.
