This is best prepared the evening before and left in the freezer overnight.
To make the quince sauce
Place 50g of the sugar and the chopped quince into a small heavy-bottomed pan. Add 750ml of water, and bring to the boil. Turn the heat down so the quince simmers gently.
Partially cover with a lid and leave to cook, testing occasionally for tenderness – make sure it is completely tender before removing the pan from the heat.
Pass through a sieve and pour the juices back into the pan. Add the remaining sugar and the pectin and mix together. Place back on the heat and begin to bring back to the boil, removing from the heat just before it boils.
Pass through a sieve again, set aside and allow to cool. Take a shallow ice cube tray and pour the mix into 12 of the cubes, then place in the freezer for 12 hours.
To make the biscuit base
Heat the butter in a small pan until it has completely melted. Crush the biscuits into small pieces in a bowl. Add the melted butter and mix well together.
To make the cheesecake filling
Melt the white chocolate over a bain-marie. You need to make an Anglaise sauce. To do this, whisk the egg yolk and caster sugar together until they become smooth.
Heat the milk in a small, heavy-bottomed pan, until it bubbles slightly at the edges, then add the mixed egg yolk and caster sugar, whisking constantly until the mixture coats the back of a spoon.
Add the melted white chocolate and the gelatine to the mixture, and mix together.
Add the mascarpone cheese and then the whipped double cream and continue to mix until completely smooth. Take off the heat.
To assemble the dish
Once the quince syrup is frozen, you can begin to assemble the dish.
Take four cylinders and place on a tray. At the bottom of each cylinder, spread a small layer of the biscuit base.
Add the cheesecake mix to a piping bag then pipe in a layer of the cheesecake mix and smooth over.
Add a cube of the quince sauce, then cover with another layer of cheesecake mix and repeat three times, smoothing the final layer of cheesecake mix over the top, then place in the freezer to set for four hours.
Heat the 300g of white chocolate and 300g cocoa butter in a bain-marie until it is completely melted. Remove the cheesecakes from the freezer, and carefully remove the cylinders. Pour a layer of white chocolate and cocoa butter mix over each cheesecake and allow to cool, then trim away any spills.
To really impress you can serve the cheesecake with a white chocolate tuile formed into a ribbon, sorbet, quince jelly, walnut praline squiggles on the plate and a candied walnut.