Preheat your oven to 350°F (175°C). In a bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Stir until it resembles wet sand. Press firmly into the bottom of a 9x13-inch baking pan. Bake for 10 minutes, then allow to cool.

In a clean bowl, whisk together pumpkin puree, heavy cream, eggs, granulated sugar, vanilla extract, and pumpkin pie spice until smooth. Pour over the cooled crust, spreading evenly.

In another bowl, beat softened cream cheese until creamy, then mix in egg yolk, additional sugar, and a splash of vanilla extract. Mix until smooth. Dollop this mixture on top of pumpkin layer and swirl with a knife.

Place in the oven and bake for approximately 40 minutes, until the edges are set and center jiggles slightly. Watch to avoid overbaking.

Cool at room temperature for about 2 hours, then refrigerate for at least 4 hours or overnight before slicing.

Slice the chilled bars into squares. Serve cold or at room temperature, optionally topped with whipped cream and cinnamon.