Prepare the pan. Arrange a rack in the center of an oven, then preheat to 325F. Line an 8x8 baking pan with two sheets of overlapping perpendicular parchment paper, leaving an overhang on all sides. Use your hands to press the parchment down into all corners, then coat with baking spray.
Make the crust. In a large bowl, combine 1 cup (120g) graham cracker crumbs, 5 Tbsp (71g) melted, cooled butter, ¼ cup (50g) brown sugar, and ¼ tsp kosher salt. Stir until very well mixed. Pour out into the prepared baking pan, then press firmly into a flat even layer.
Bake the crust. Transfer to the preheated oven, then bake for 10-12 minutes, or until set. Remove from the oven, then allow to cool slightly while you make the filling.
Make the cheesecake filling. Beat 1 lb (454g) cream cheese, ⅔ cup (150g) sugar, and 2 tsp vanilla extract in the bowl of a stand mixer fitted with paddle attachment until smooth and creamy, about 2 minutes. Scrape down the sides, then add 2 large eggs. Continue beating on medium-low until fully incorporated and the mixture is fluffy. Pour half of the cheesecake filling on top of the slightly cooled crust, then smooth into an even layer.
Make the pumpkin cheesecake filling. To the remaining cheesecake batter, add ¾ cup canned pumpkin purée, 1 tsp ground cinnamon, ¼ tsp ground ginger, ¼ tsp ground nutmeg, and a pinch of allspice. Beat until very well mixed, about 1-2 minutes more. Pour this on top of the plain cheesecake filling, then smooth into an even layer.
Bake the cheesecake bars. Transfer to an oven, then bake for 30-40 minutes, or until the filling is set, rotating the pan once halfway through cook time.
Cool. Place the pan on a wire rack, then cool at room temperature for at least 2 hours. Cover with plastic wrap or foil, then refrigerate for at least 6 hours or up to overnight.
Slice, then serve. When ready, carefully use the parchment to lift the cheesecake bars out of the pan. Cut into 16 bars, then serve immediately! I like to dollop or pipe a little homemade whipped cream on each, sprinkle with the tiniest bit of ground cinnamon. Optional, but so good!