Preheat the oven to 180ºC/350ºF/gas ,

Blitz the biscuits in a food processor into fine breadcrumbs.,

Melt the butter in a saucepan on a medium-low heat, then combine with the crushed biscuits.,

Spoon the biscuit mixture into a loose-bottomed 25cm tart tin, then use the back of a spoon to spread it evenly over the base and up the sides of the tin until it’s completely covered.,

Bake in the oven for 8 minutes, then leave to cool while you prepare the filling.,

In a large bowl, beat the cream cheese, sugar and vanilla extract until smooth, then gradually beat in 250ml of the cream until fully combined and silky.,

Snap the dark and white chocolate into separate bowls, each set over a saucepan of simmering water. Divide the remaining cream between the bowls and allow the chocolate to melt, stirring occasionally.,

Fold the melted dark chocolate into the cream cheese mixture until smooth and well combined, then pour into the cooled tart case.,

Drizzle the melted white chocolate over the top, then use a chopstick or a skewer to swirl it into pretty patterns.,

Leave in the fridge for at least 2 hours, or until set. Cut into slices and serve.