1.Line each hole of a greased six-hole (¾-cup/180ml) texas muffin pan with plastic wrap. Chop biscuits into 1cm pieces; divide among pan holes.
2.In a small heatproof jug, sprinkle gelatine over the water. Stand jug in small saucepan of simmering water; stir until gelatine dissolves, cool 5 minutes.
3.In a small bowl, beat cream cheese and sugar with electric mixer until smooth; beat in cream until combined. Stir in gelatine mixture, chocolate bar and nuts.
4.Divide mixture among pan holes; smooth surface. Refrigerate overnight.
5.In a small saucepan, combine chocolate and extra cream; cook, stirring, over low heat until smooth.
6.Lift cheesecakes from pan, remove plastic wrap; turn, top-side up, onto plates. Drizzle with chocolate sauce.