Beat the egg yolks and sugar together in a medium bowl until thick and pale. Add the mascarpone, cocoa and dark chocolate, mixing it well until well blended. Fold the whipping cream using an electric mixer. Add to the egg and mascarpone batter, stir to combine.
Pour-in 2 or 3 tbsps mascarpone mixture in a deep 20x27 cm serving dish. Combine coffee and brandy in a small bowl. Dip half the biscuits, one at a time, in the coffee moisten. Arrange in a single layer in dish. Spread with 1/3 of the mascarpone mixture. Repeat 2 layers.
Cover with cling wrap or aluminum foil and refrigerate for at least 5 hours.
To serve, dust generously with cocoa and sprinkle white chocolate on top.
