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Preheat the oven to 200˚C and check you have a roasting tin big enough to accommodate a 9 inch cake tin.
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Prepare the base by pulsing the biscuits and butter in a food processor until finely chopped then tip into a 9 inch spring form pan and press down firmly to flatten. Wrap the base in two large overlapping pieces of foil and place in the fridge.
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Clean out the processor and start by processing the chestnut purée and caster sugar until well incorporated then add the cream cheese and repeat. Add the rest of the ingredients for the filling and process until smooth.
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Retrieve the cake tin from the fridge and pour over the cheesecake batter (I sometimes do this through a sieve to ensure there are no lumps but it's not crucial).
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Place the foil wrapped pan in a deep roasting dish and carefully, pour in enough boiling water from the kettle to come up just over half way up the sides of the tin. Take care not to splash and water inside the tin.
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Place in the oven and bake for 60 minutes, checking with 10 minutes left to go that the centre of the cheesecake retains a hint of inner thigh wobble. If it does, turn off the oven but leave the cheesecake in for half an hour with the door shut.
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Next, crack open the oven door with a wooden spoon and leave another half an hour then remove to a baking rack to finish cooling, discarding the foil at this point too.
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Once room temperature, cover the tin with cling film and refrigerate overnight before releasing from the spring form tin and transferring to a serving plate (leave it on the base if you're worried about transferring it off that to a plate).
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Whip the double cream and seeds of the vanilla bean until thick but not stiff and pipe 10 rosettes or dollop on around the edges of the cheesecake. Scatter with the chocolate chips and break up a marron glacé or two to adorn the top of the whipped cream rosettes.
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Eat within 48 hours or freeze in the tin for upto a month without the topping (thaw overnight in the fridge then proceed with topping as above).