Preheat your oven to 325°F (165°C) and line a 9x13-inch baking pan with parchment paper, leaving overhang on the sides for easy removal.
In a medium bowl, combine graham cracker crumbs, melted butter, sugar, and salt until the mixture resembles wet sand.
Press the mixture firmly into the bottom of your prepared pan, creating an even layer. Use the bottom of a measuring cup to compact the crust.
Bake the crust for 10 minutes until it's just beginning to turn golden at the edges.
In a large bowl, beat the cream cheese until completely smooth and free of lumps (about 2 minutes).
Add sugar and continue beating until incorporated. Beat in eggs one at a time, then add vanilla extract and sour cream.
In a separate bowl, whisk together pumpkin puree, brown sugar, eggs, vanilla, pumpkin pie spice, and heavy cream until smooth and well-combined.
Pour the cheesecake batter over the pre-baked crust, spreading it into an even layer.
Carefully pour the pumpkin mixture over the cheesecake layer. For a marbled effect, use a butter knife to gently swirl the two layers together with a figure-eight motion, being careful not to overmix.
Bake for 40-45 minutes, or until the center is almost set but still slightly jiggly (like the consistency of set gelatin).
Allow the bars to cool completely at room temperature, then refrigerate for at least 2 hours (though overnight yields the best flavor development).
Cut into 16 squares and serve chilled.