1.Using an electric mixer, beat 200ml of the cream with cocoa powder and half the sugar in a small bowl until soft peaks form. Stir in chopped hazelnuts.
2.Drain cherries, reserving syrup in a small bowl. Reserve 10 cherries for garnish; chop remaining cherries finely. Stir chopped cherries into cream mixture. Stir marsala into reserved cherry syrup.
3.Working with one biscuit at a time, dip into cherry syrup and spread with a heaped tablespoon of cream mixture. Sandwich with a second syrup-dipped biscuit; stand sandwich upright on a serving platter. Continue with remaining biscuits to make a log. Cover; chill log for 6 hours or overnight.
4.Using an electric mixer, beat remaining cream and sugar in a small bowl until firm peaks form. Spread cream over top and sides of log. Sprinkle with chocolate curls, extra hazelnuts and reserved cherries to garnish. Cut into thick slices (on an angle). Serve.
To prevent the log from cracking, spread whipped cream over cake before serving. Marsala is fortified wine; you can replace it with liqueur, such as kirsch (cherry) or Kahlua (coffee) if you like. Use any style of un-iced chocolate biscuit. Try well-drained frozen raspberries instead of cherries.