How to Make It
In a small saucepan, combine the sugar and 2 tablespoons of water and bring to a boil. Using a wet pastry brush, wash down any crystals on the side of the pan. Boil over high heat until a deep amber caramel forms, about 6 minutes. Remove the saucepan from the heat and carefully whisk in the cream, butter, vanilla and a pinch of salt. Let the caramel cool to room temperature.
Preheat the oven to 350° and butter a 9-by-13-inch baking pan. In a food processor, pulse the chocolate wafers with the sugar and a pinch of salt until fine crumbs form. Add the butter and process until the crumbs are evenly moistened. Using your fingers, press the crumbs into the prepared baking pan in an even layer. Bake the crust for about 10 minutes, until set. Let cool completely.
In a large bowl, beat the cream cheese with the sugar at medium speed until blended. Beat in the pumpkin puree, sour cream and vanilla, then beat in the eggs until just incorporated. Transfer 1/3 cup of the cheesecake batter to a small bowl and stir in the caramel sauce.
Set the pan with the crust in a large, deep roasting pan. Pour the pumpkin cheesecake filling over the cookie crust and carefully drizzle the caramel mixture over the top. Using a toothpick, decoratively swirl the caramel sauce. Transfer the roasting pan to the oven and carefully pour in enough hot water to reach halfway up the side of the baking pan. Bake the cheesecake for about 55 minutes, until the filling is barely jiggly in the center. Transfer the roasting pan to a rack and let the cheesecake cool completely. Remove the baking pan from the water bath and refrigerate the cheesecake overnight. Cut into bars and serve.