After peeling and mincing the persimmons process them in a food processor until you have a velvety smooth puree.
Heat the persimmon puree in an appropriate sized saucepan over medium-high heat and add the brown sugar. Stir steadily and persistently in order to meld the sugar and puree and avoid coagulation and separation.
Boil for about 15 minutes on a slow rolling boil , stirring constantly.Heat should not be excessive - so as to avoid scorching.
Mix the corn starch with a small amount of water until it is completely dissolved.
Combine the corn starch with the persimmon puree and juice of one lemon. Boil it on low heat for another 15 minutes until slightly thickened.
Allow the jam cool to room temperature.