Combine the heavy cream, vanilla, and half the sugar, bring to a boil. Combine the egg yolks and remaining sugar. Add 1/3 of the hot liquid to the egg mixture, stir constantly. Add the egg yolk mixture to the remaining hot cream, stir constantly. Stir in the cinnamon, allspice, and ginger. Fold in the pumpkin puree. Fill buttered oval ramekins 7/8 full, place in a waterbath. Bake in a 325°F (160°C) oven until just barely set, cool 30 minutes, chill overnight. Cover the surface of each custard with 1/8-inch of sugar, set ramekins in a hotel pan, surround with ice. Carmelize sugar under the broiler or with a torch.