SERVES 6
Whisk the 4 egg yolks with the sugar t and vanilla essence in the top of a double saucepan or in a heatproof bowl set over a saucepan of barely simmering water. When the mixture is pale and so thick that the whisk leaves a ribbon trail when lifted, remove the bowl from the heat and set aside to cool completely. Cover with cling film or whisk the mixture occasionally to prevent a skin from forming
When the egg yolk mixture is quite cool whisk the mascarpone into the egg yolk mixture until thoroughly combined. With clean blades, whisk the egg whites in a separate, spotlessly clean, bowl until they form soft peaks, then gently fold them into the mascarpone mixture with a figure-of-eight action,
Combine the coffee and liqueur, rum or brands in a shallow dish. Dip the Savoiardi, boudoir or sponge fingers into the mixture, one at a time, turning them quickly so that they absorb the liquid but do not fall apart. Arrange a layer of biscuits on the base of a serving dish.
Spoon about one-third of the mascarpone mixture on top, spreading it out evenly. Repeat the layers, dipping and turning the biscuits quickly in the coffee mixture. Finish with a layer of the mascarpone mixture and smooth the surface. Chill for at least 1 hour or preferably, overnight before serving
Just before serving, sift the cocoa powder evenly over the top of the dessert, then sprinkle with the grated chocolate
