Place the persimmon jam and lemon juice in a pan, cover and simmer for approx. 5 mins. until soft, puree and pass through a sieve. Add the preserving sugar, bring to the boil, cook on a rolling boil for approx. 2 mins., leave to cool.
Beat the chestnut puree and half of the whipped cream with a whisk until smooth. Carefully fold in the remainder of the whipped cream.
Carefully fold the persimmon mixture into the chestnut mixture using a fork to create a ripple effect, cover and chill for approx. 2 hrs.