Butter 2 x 20cm (8in) springform cake tins and line the base of each with a disc of buttered baking paper. Dust the insides with plain flour.
Preheat the oven to gas 4, 180ºC, fan 160ºC. Melt the butter in a pan and set aside to cool slightly.
Using a mixer on medium-high speed or a hand whisk, beat the eggs, sugar and vanilla extract until the mix has trebled in volume.
Sift together the plain flour, baking powder and a pinch of salt. Using a large metal spoon, fold the flour into the egg mixture. Pour the melted butter around the edge of the bowl and gently fold in.
Divide the batter between the prepared tins. Spread level and bake on the middle shelf of the oven for 15 minutes or until golden and risen. When done, a skewer inserted into the cake should come out clean. Cool in the tins for a few minutes, then turn out onto a cooling rack.
To prepare the coffee syrup, pour the hot coffee into a bowl, add the sugar and stir until dissolved.
To make the filling, whisk the egg yolks, sugar, Marsala and a pinch of salt in a bowl. Set over a pan of simmering water and continue whisking for about 5 minutes until the mixture is heated through, thick and tripled in volume. Remove from the heat and plunge the bottom of the bowl into cold water. Whisk until cold.
Melt the white chocolate in a bowl over a pan of just simmering water or in the microwave on a low setting. Stir until smooth and leave to cool slightly. Beat the mascarpone until smooth and fold into the egg mixture with the melted white chocolate.
Slice the cakes in half horizontally using a bread knife. Put one cake layer in the bottom of a 20cm (8in) springform tin, brush with the coffee syrup and spread on 3 tablespoons of the mascarpone mixture. Scatter with 1 tablespoon of grated dark chocolate. Repeat this layering until you end with the fourth cake layer. Cover with clingfilm and chill for at least 2 hours. Chill the leftover mascarpone mixture.
Turn the cake out onto a serving plate or cake stand. Spread the top and sides with the remaining mascarpone mix. Press the crushed amaretti biscuits onto the sides, dust the top with cocoa and decorate with chocolate-coated coffee beans or Minstrels.