In a small bowl, sprinkle the gelatin over the water and let stand for 5 minutes. In a large bowl, whisk the yolks, cornstarch, salt and 1 1/2 cups of the sugar until the sugar is moistened. In a large saucepan, heat the milk just until steaming. Whisk 1 cup of the hot milk into the yolk mixture. Pour the mixture into the milk in the saucepan and cook over moderate heat, whisking constantly, until boiling and thick, about 5 minutes. Whisk in the pumpkin puree and cook, whisking, for 1 minute. Off the heat, whisk in the gelatin, vanilla and cinnamon. Whisk in the mascarpone.