The first thing you’ll need to do is make a tin foil ‘jacket’ for the cake tin. This is because when you come to bake it, you will place the cake tin into a large dish of water to cook. This is called a bain-marie (a water bath). This controls the temperature and importantly, stops the cheesecake from cracking. The tin foil jacket makes the tin waterproof during this process. To make the jacket, stand the cake tin on a piece of tin foil and bring the edges up, but don’t tuck them into the inside of the tin. Repeat with a several sheets of foil. When you’ve finished, take the tin out of its jacket.
Grease the inside of the tin with a little butter.
Then make the base. Melt the butter over a low heat. While it is melting, weigh up your biscuits and turn them into fine crumbs. If you have a food processor use this, otherwise put them in a plastic back and crush them with a rolling pin. Place your shelled pistachios on a baking tray and roast in the oven for about 5 minutes. Give the tray a shake half way through and keep an eye on them to make sure they don’t burn. Allow the nuts to cool and crush finely, either with a food processor or a mortar and pestle.
Add the nuts to the crumbs and then pour over the melted butter and mix well. Press these into the bottom of the greased cake tin. You want to make sure the base is well-compressed so press hard. Then bake without the foil jacket for 8 minutes.
Time to start on your filling. Zest the orange very finely and set this aside. Keep the orange handy so you can squeeze out the juice which you’ll need shortly. To prepare the cardamom, use a knife to take out the seeds in the middle. Discard the green husks. Finely crush the seeds in a mortar and pestle. Set aside for later.
Put the white chocolate into a bowl above a saucepan of hot water and allow to melt slowly. Avoid over-stirring or overheating the chocolate or it will turn grainy. Remove from heat as soon as it's melted In a large mixing bowl, mix the cream cheese until creamy. If you have an electric whisk, use this on the lowest setting. If not (I didn’t) a wooden spoon does the trick. Then add the sugar and orange juice and mix until smooth, making sure you scrape down the sides to capture all of the mixture. Then add the flour and cardamom and stir in. Beat the eggs and add them in gradually. Finally stir in the cream. By now it should be a thick consistency.
Finally pour in the chocolate – you need to do this quickly to prevent it setting and going lumpy. Keep stirring until all the ingredients are combined and you have a glossy mixture.
Now put the tin into its foil jacket and place it into a large baking dish. Pour the mixture onto the cooked base and level with a spoon – it should come right to the top. Now carefully pour hot water into the baking tin so it comes about 3cm up the side of the foil.
Place into the oven for 1 hour and 15 minutes. When it's ready, the cake will be golden brown on top. The top will have set but the cake will be wobbly to the touch – don’t worry; it will set when it cools.
Remove the cake from the oven. Cover the top gently with a sheet of kitchen roll and leave it to cool in the water bath for an hour. The reason for this is that it cools the cake down very slowly and therefore prevents the top from cracking. Remove from the water bath and cool and refrigerate for at least four hours, still in the tin.
While the cake is cooling make your syrup. In a saucepan, stir together the orange juice and the sugar over medium high heat until the sugar dissolves and the mixture comes to a boil. Reduce the heat Roast the remaining pistachio nuts in the same way as those used for the cake. Allow to cool and chop very coarsely.
When you are ready to serve, gently remove the cake from the tin and cut into slices. Pour some of the syrup over the top and sprinkle a few of the roasted pistachios and a couple of strands of orange zest.