1.Dissolve coffee and half the sugar in the water in medium heatproof bowl. Stir in liqueur; cool.
2.Meanwhile, beat cream and remaining sugar in small bowl with electric mixer until soft peaks form; fold in mascarpone.
3.Dip biscuits, one at a time, in coffee mixture; place in single layer in shallow 2-litre (8-cup) serving dish. Pour any remaining coffee mixture over biscuits.
4.Spread cream mixture over biscuits; sprinkle with combined nuts and chocolate. Refrigerate until required.