Grease a 20cm x 30cm rectangular pan and line base and long sides with baking paper, extending paper 5cm over sides.
Process biscuits until fine. Add melted butter; process until combined. Press mixture over base of pan and refrigerate 30 minutes.
Meanwhile, sprinkle gelatine over the water in a small heatproof jug. Stand jug in small saucepan of simmering water. Stir until gelatine dissolves. Cool 5 minutes.
Beat cream cheese and sugar in a medium bowl with electric mixer until smooth. Beat in cream until smooth and thickened slightly. Stir in gelatine mixture and liqueur. Pour filling into pan and refrigerate overnight or until set.
To make chocolate glaze, combine chocolate and butter in a small saucepan. Stir over low heat until smooth. Pour over slice, refrigerate until set before cutting.