In a food processor, blend the ginger snaps until coarsely ground. Add the 4 tablespoons melted butter, dashes of cinnamon, nutmeg and cloves, and process until the butter is distributed. Pour the crumbs into a deep pie dish and press into the bottom and the sides. Bake at 325F for 12 to 15 minutes. Remove from the oven, and increase the oven temperature to 350F.

In a medium pot, place a steam basket and 1 to 2 inches of water. Put the sweet potatoes in the basket, cover, and steam for about 15 minutes. Allow the sweet potatoes to cool slightly. Transfer to a large bowl. Using a hand mixer, blend the sweet potatoes until they are well pureed. Add the softened butter and sugars, and blend. Add the eggs, buttermilk, remaining spices, and vanilla, and blend on low until completely mixed.

Transfer the filling to the cooled pie crust. Bake at 350 degrees for 1 hour and 25 minutes (it will still be slightly jiggly in the center). Serve at room temperature, or cold.