Preheat oven to 180C (160C fan). Grease a 13cm x 36cm rectangular tin.

Place the biscuits and melted butter in the bowl of a food processor and blend until the mixture resembles wet sand. Place this mixture in the tin and press firmly over the base and sides of the tin.

Bake in the oven for 10-12 mins or until firm. Allow to cool completely.

Meanwhile, place the cream cheese, sugar and vanilla extract in the bowl of an electric mixer, beat until smooth.

Add the eggs, one at a time, beating well between each addition. Divide the mixture into 2 equal amounts.

Add the melted chocolate to one portion. Spoon alternate amounts of the chocolate and vanilla mixture into the tin over the biscuit layer and then, using the end of a spoon, swirl the two mixtures to create a 'ripple' effect.

Bake for 20-25 minutes or until just wobbly in the center. Cool and serve.