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 ½ 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.
In a small microwave-safe bowl, microwave the Calvados with the remaining 1 tablespoon of sugar at high power for 10 seconds, just until the sugar is dissolved.
Arrange one-third of the whole gingersnaps in a 9-by-13-by-2 ½-inch baking dish.
Lightly brush the gingersnaps with some of the Calvados and top with one-third of the pumpkin custard.
Repeat the layering twice more with the remaining whole gingersnaps, Calvados and custard.
Sprinkle half of the crushed gingersnaps on top and press a sheet of plastic wrap directly on the surface of the tiramisù.
Freeze overnight.
Let the tiramisù stand at room temperature for 6 hours, until thawed.
Sprinkle with the remaining gingersnaps.
Serve.
