In a bowl, sprinkle gelatin over water and let stand for 5 minutes. In a separate bowl, whisk yolks, cornstarch, salt and 1 1/2 cups of the sugar until blended. In a large saucepan over medium heat, warm milk just until it begins to simmer. Temper the egg mixture with the hot milk, then pour the mixture into the saucepan and cook over medium heat, whisking constantly, until boiling and thick, about 5 minutes. Add pumpkin puree and cook, whisking, for 1 minute. Remove from heat and whisk in gelatin, vanilla, cinnamon, and mascarpone.

In a small saucepan, heat the brandy with remaining
sugar until sugar dissolves. Remove from heat and add Christmas Ale. Dip gingersnaps in the
Christmas Ale mixture and arrange one-third of them in a 9×13 baking dish. Top with one-third of the
pumpkin custard. Layer twice more with remaining gingersnaps, Christmas Ale mixture, and custard.
Top with an overlapping layer of gingersnaps and press a sheet of plastic wrap directly on the surface
of the tiramisu. Freeze overnight, then let stand at room temperature for 6 hours before serving.