For the blondie base: Adjust oven rack to middle position; heat oven to 350° F. Line a 8-inch round cake pan with foil, leaving enough overhang to help you lift the blondies from the pan when they're done. Grease foil-lined pan with butter or oil. Whisk flour, baking powder, pumpkin pie spice and salt together in medium bowl; set aside. Whisk melted butter and brown sugar together in medium bowl until combined. Add the egg and vanilla and mix well. Using rubber spatula, fold dry ingredients into egg mixture until just combined; do not overmix. Fold in chocolate chips and spoon batter into prepared pan, smoothing top with rubber spatula. Bake until top is shiny, cracked, and light golden brown, 22 to 25 minutes; do not overbake. Cool on wire rack to room temperature. Remove bars from pan by lifting foil overhang and wrap in plastic wrap until ready to assemble the dessert.
For the cheesecake: Line the bottom of an 8-inch springform pan with parchment paper. Set aside. Using an electric mixer, beat the cream cheese and 3/4 cup sugar on medium-high speed until light and fluffy, about 2 minutes. Scrape down the bowl. Beat in the eggs 1 at a time, beating well after each addition. Add the pumpkin puree, sour cream, vanilla and pumpkin pie spice; beat until combined. Sprinkle the flour over the mixture and beat on low speed until just combined.
Place the springform pan on a baking sheet and pour the filling into the shell. Bake for 15 minutes. Lower the oven temperature to 250 degrees and bake for 1 hour longer. Turn off the oven and let the cheesecake cool in the oven with the door ajar for 2 1/2 hours. Transfer to a rack and let cool to room temperature. Refrigerate uncovered until thoroughly chilled, at least 10 hours or up to 2 days. Remove the side of the pan and let sit at room temperature for an hour. To serve, remove the parchment paper and place the cheesecake on top of the blondie base. To cut the cheesecake into wedges with a sharp knife thats been dipped in hot water and wiped clean after each cut. Serve the cheesecake slightly chilled or at room temperature with whipped cream and caramel sauce if you so choose!