Make the coffee. You can also use Camp Coffee syrup. When cool, add the rum.
Whisk the egg yolks and sugar together. Add the mascarpone. If using cream, whisk it until thick.
Whisk the whites together until thick and cloudy.
Fold the white into the egg yolk/cream mixture.
Dip the biscuits into the coffee mixture. Do it briefly or they fall apart.
Add in layers to the glass dish. Alternate a layer of biscuits, then a layer of cream mixture.
Dust with cocoa or chocolate powder on top of the cream layers.
Finish with a cream and cocoa layer.
Chill in the fridge for 24 hours at least.
Serve cold with coffee.