Have all your ingredients at room temperature for best results.
Make the base
Crumble the biscuits to a fine crumb. You can do this either by blitzing them in a food processor until sandy or by placing in a bag and bashing with a rolling pin.
Pour in the melted butter and mix well.
Empty the mixture into a loose-bottomed non stick tin and press down with the bottom of a tumblr until even and firm.
Cook in the oven for just 5 minutes - set a time so that you don't burn it. Take it out of the oven and set it aside.
Make the filling
Melt the dark chocolate and set aside to cool.
Put the cream cheese in a large bowl and work with a spatula to loosen. We don't want to introduce too much air to this filling, so don't beat vigorously.
Add the eggs, vanilla, sugar and flour, then work with the spatula again, just enough to give a smooth mixture.
Finally, add the cream and again, stir gently together. This is your vanilla cheesecake mixture.
Transfer quarter of the mixture to another bowl and add the cooled melted chocolate and salt to this smaller portion.
Mix together. The is your chocolate cheesecake mixture.
Assemble your cheesecake
Pile half of the vanilla cheesecake mixture into the tin, gently working to the edges.
Spoon the chocolate cheesecake mixture on top in blobs, keeping a tablespoon back.
Gently swirl to the edges.
Pile the remaining vanilla cheesecake mixture on top
Push the handle of a metal spoon into the filling, making sure not to go so deep as to disturb the biscuit base. Swirl back and forth with the spoon to create swirls inside the cheesecake.
Use the tablespoon of chocolate cheesecake mixture you reserved to dot a few drops over the top of the cheesecake and mix using shallow swirls to give a pretty effect on top.
If you have a baking belt, this is a great time to use it. It's a piece of material you soak in water and then wrap around the outside of the tin to stop cakes, cheesecakes and more from baking too fast on the outside before the middle is cooked. It's not essential for this recipe, but it does help ensure an even bake with no cracks.
Your marble cheesecake is now ready to bake in the oven for approximately 1 hour until set but still wobbly. The top will darken and turn a gleaming golden.
Take out the oven, and let it cool for 5 minutes. Run a knife around the edges of the cheesecake. This will ensure it doesn’t stick, causing the cheesecake to come apart as it cools.
Allow to cool completely in the tin at room temperature.
Release from the tin and chill in the fridge for at least an hour, but ideally overnight (or as long as you can stand to wait).
Slide the sides of the tin down to release the cheesecake, then transfer to a board to serve.
All that's left to do is slice and enjoy! This is best done with a warm knife for a clean cut.