Preparation -
Butter and flour a 10-inch springform cake pan. Mix the gingersnap crumbs with the melted butter. Press the crumbs into the bottom of the springform pan. Bake in a preheated oven at 350º for 10 minutes. Remove from the oven and cool on a wire rack. Lower the oven temperature to 325º.
Meanwhile, in a large mixing bowl, at medium speed with an electric mixer, beat the cream cheese until smooth. Beat in the brown sugar and 3/4 cup of the granulated sugar. Add the eggs and beat until thoroughly mixed, while scraping sides of bowl. Set aside. In a separate bowl, combine the pumpkin, whipping cream, 1 teaspoon vanilla, cinnamon, ginger and nutmeg. Beat at medium speed until well blended. Add to the cream cheese mixture and beat again until well blended.
Loosely wrap aluminum foil around the bottom and up the sides of the cake pan to prevent any water from seeping into the batter (Since the filled cake pan will be placed in a shallow pan of water to bake). Pour the cheesecake batter into the prepared cake pan. Place the filled cake pan inside a shallow broiling or roasting pan. Pour warm water, about 1" deep, into the broiling or roasting pan. Place the cake pan, sitting in the pan of water, in the oven and bake at 325º for about about 70 minutes. Remove from the oven and remove from the pan of water. Place the cake, in the springform pan, on a wire rack to cool.
In a small bowl, combine the sour cream, the remaining 1/4 cup sugar and the remaining 2 tsp. vanilla. Pour the sour cream mixture over the baked cheesecake. With a spatula or the back of a spoon, very gently spread the mixture over the cheesecake. Return the cheesecake to the oven and bake for 10 more minutes.
Remove the cheesecake from the oven. Cool on a wire rack for 1 hour. Remove the aluminum foil. Remove the side of the springform cake pan from the cheesecake, letting the cake remain on the bottom of the pan. Refrigerate for at least 4 hours before serving.