Chocolate pie shell: Put butter, into a 1 liter microwave safe bowl. Microwave, uncovered, on high (100% ) for about 35 seconds until melted. Stir inn wafer crumbs and sugar until well mixed. Press into bottom and up sides of 9 inch (22cm) glass pie plate. Microwave, uncovered, on high (100%) for 2 minutes.

Filling: Beat cream cheese and sugar together in large bowl until smooth. Beat in eggs 1 at a time, beating well after each addition. Add liqueur. Mix. Pour into pie shell. Cover with waxed paper. Microwave on medium (50%) for about 10 minutes, until middle is set. Cool.

Topping: put chocolate chips into 1 cup (250ml) liquid measures, microwave, uncovered, on medium (50%) for 2 minutes. Stir until smooth. Add sour cream. Stir, spread over filling. Chill for 3-4 hours until set