Dissolve 2 tablespoons of instant coffee in 300ml of boiling water. Leave to cool.
Whisk 568ml of heavy cream, 250g of mascarpone, 75ml of Marsala, and 5 tablespoons of superfine sugar until thick and holding soft peaks.
Take 175g of ladyfingers. Briefly dip half in the coffee and lay them in a dish; avoid soaking until soggy.
Spread over half the cream mixture. Grate most of 25g of dark chocolate over it. Repeat the layers with the remaining dipped ladyfingers and cream mixture.
Cover and refrigerate for at least 4 hours. Before serving, dust with 2 teaspoons of cocoa powder and grate the remaining chocolate on top.
