In a large metal bowl, place yolks and sugar, place the bowl on a pot of simmering water and continue to whisk, cooking the mixture until the colour turns pale yellow and is doubled in volume, should take about 5-6 minutes; to this add mascarpone, vanilla, salt and melted chocolate, stir until well combined.
Whip double cream until stiff peaks form, fold into the chocolate mixture and set aside. In a bowl mix together coco powder and hot water.
One at a time dip savoiardi in coco liquid and line the bottom of the serving bowl, top with half the chocolate filling, repeat. spread remaining chocolate filling, refrigerate until ready to serve. Dust coco powder before serving.
