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1
Make the crust: Preheat oven to 325F.
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2
In a food processor, combine graham cracker sheets, sugar, cocoa, cinnamon, and nutmeg; process until finely ground.
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3
Transfer to a medium bowl; mix in butter.
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4
Press mixture into bottom and up sides of a 10-inch tart pan with a removable bottom.
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5
Place on a parchment-lined rimmed baking sheet; bake until dry, 12 to 15 minutes.
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6
Let cool completely on a wire rack.
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7
Make the filling: In a small heatproof bowl, combine brandy and 2 tablespoons water.
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8
Sprinkle gelatin over liquid; let soften 10 minutes.
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9
With an electric mixer on medium-low, beat eggs.
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10
While eggs are beating, combine remaining 1/4 cup water and the granulated sugar in a small saucepan over medium-high heat.
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11
Cook, stirring occasionally, until mixture registers 245F on a candy thermometer, about 5 minutes.
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12
Immediately raise mixer speed to high.
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13
Pour sugar mixture down side of mixing bowl in a thin stream; whisk until mixture increases in volume and is pale yellow, about 5 minutes more.
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14
Place bowl with softened gelatin over (not in) a pan of simmering water; stir until gelatin has dissolved.
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15
Reduce mixer to low speed; whisk in gelatin mixture, the pumpkin, sour cream, allspice, ginger, cinnamon, nutmeg, and salt.
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16
Pour into piecrust; refrigerate until set, 4 hours or up to 1 day.
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17
Make the topping: Whisk cream, confectioners sugar, and vanilla in a medium chilled bowl until stiff peaks form.
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18
Using a pastry bag fitted with a 7/16-inch star tip (such as Ateco #825), pipe whipped cream over tart.
