Tirami Su (pick me up)

Serves 4. Put the egg, sugar and vanilla in a bowl and mix gently to a creamy consistency. Add the mascarpone and fold in to obtain a cream. Put the coffee in a bowl with the coffee liqueur. Dip the biscuits for a second or two in the coffee mixture, letting them absorb just enough to keep firm but not fall apart. Starting with the biscuits, arrange in four individual dishes alternating layers of biscuits and mascarpone, ending with mascarpone. Dust with cocoa powder and put into the fridge to set and chill.