Bash the biscuits in a resealable bag with a rolling pin until you have fine crumbs.
Melt the butter in a large saucepan then add the biscuit crumbs and mix to combine. Tip the butter and biscuit mix into the base of a lined 20cm/8" cake tin. Pack in the biscuit mix with a spoon or a meat mallet.
Place the chocolate in a heatproof bowl, in a single layer if you can, over a pan of barely simmering water, making sure the base of the bowl does not touch the water, and gently melt, without stirring. You can tell it is melted when you gently nudge a square and it will dissolve. Only then stir together and set aside.
Beat the cream cheese, cream and mascarpone in a large bowl with an electric hand whisk, then, with a spatula, stir through the white chocolate and pour over the biscuit base in the tin.
Dollop the pureed raspberries over the top of the cheesecake and using a spoon, swirl the raspberries into the cream mix. Dot in the remaining whole raspberries, lightly pushing them into the mix.
Cover and place in the fridge to chill and set for at least 2 or 3 hours.
Remove the cheesecake from the tin and cut into bars then serve.