To prepare the sponge, whisk the eggs together with the caster sugar until it has increased in bulk into a creamy pale consistency. Whisk in the hot water. Sift the flour baking powder together and fold carefully into the egg mixture. Line a 30×40 cm baking tray with baking paper and carefully spread the chocolate sponge on top. Bake in a hot pre heated oven at a temp of 180 c for approximately 15 minutes. Take out of the oven and allow to cool completely before proceeding. Meanwhile, prepare the cream. Chop the chocolate and melt over a bain-marie together with the milk. Remove from heat, add the liquor and allow cooling completely. Fold in the mascarpone cheese and then the whipped cream and put aside. To assemble, turn the chocolate sponge sheet onto a clean baking paper. Spread with 2/3 of the chocolate and roll with the aid of the paper, pressing tightly. Roll and shape neatly with the aid of the paper. Transfer onto a serving tray; Spread roll with the remaining cream and cover with the chocolate shavings. Dust with icing sugar. Keep in a refrigerator for 1 hour before serving.