Make the coffee and pour into a shallow dish along with the Marsala, or similar, if using. Add the amaretti biscuits and leave to soak for a couple of minutes.
Separate the eggs. Beat the egg yolks with the sugar on a high speed until pale and creamy, and a ribbon trail is left when you pull the whisk away. Add the mascarpone and beat again until smooth.
In a separate bowl, whisk the egg whites to firm peaks. Fold into the mascarpone mixture 1/3 at a time.
Put half of the amaretti biscuits into a serving dish, or 4 individual dishes or ramekins. Cover with half of the creamy mixture. Put the rest of the amaretti on top, and cover with the rest of the creamy mixture. Dust with cocoa powder and leave in the fridge for at least an hour before serving. If using dark chocolate shavings instead, sprinkle over just before serving.