Cover a 9 inch springform tin with a double layer of foil on the outside and check you have a roasting tin big enough and deep enough to take the cheesecake with an inch or two of water all around it. Process your digestive biccies to a fine crumb then add in the chopped chocolate, melted and cooled butter and process until fully incorporated.

Tip into the prepared tin and press into an even layer – pop in the freezer whilst you make the cheesecake.

Beat your sugars and room temp cream cheese until smooth and the sugar granules dissolved then add in the vanilla then all the eggs, incorporating one well before adding the next.

Follow with the cooled melted dark chocolate, making sure the mixture is super smooth and silky.

Pour the cream cheese mix on top of the biscuit base then transfer to the roasting dish and carefully pour boiling water from a kettle around the tin in its baking dish to come up about half way.

Carefully slide onto a middle shelf of the oven (it will be very heavy) and bake for 1 hour – it will still be wobbly in the middle (if it’s very wobbly, bake an extra ten minutes before adding the topping)

Just before the cheesecake is ready, pop your sour cream and white chocolate into a small saucepan and melt gently – then pour in a steady stream over your cheesecake just holding the pan over the centre – it should spread out to fill the whole surface (coax with a spatula if necessary).

Return to the oven for 10-15 mins until, as Nigella would say, the centre of the cheesecake has a hint of inner thigh wobble then remove from the oven.

Take out of its water bath and cool on a rack – when reaches room temp, pop in the fridge to fully chill, over night if you can wait that long.