Preheat oven to 350°F (175°C).
Line an 8×8 inch baking pan with parchment paper, leaving an overhang on the sides.

Prepare the Crust:
In a medium bowl, combine graham cracker crumbs and granulated sugar.
Pour in the melted butter and mix until well combined.
Press the mixture evenly into the bottom of the prepared baking pan.
Bake for 8-10 minutes until lightly golden. Remove from oven and set aside.

Prepare the Pumpkin Cheesecake Filling:
In a large bowl, beat the softened cream cheese and granulated sugar until smooth and creamy.
Beat in the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract, pumpkin pie spice, cinnamon, and nutmeg.
Add the pumpkin puree and mix until just combined. Be careful not to overmix.
Pour the filling evenly over the baked crust.

Prepare the Streusel Topping:
In a small bowl, combine flour and brown sugar.
Cut in the cold, cubed butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.
Sprinkle the streusel topping evenly over the pumpkin cheesecake filling.

Bake:
Bake for 35-45 minutes, or until the edges are set and the center is almost set (it should still have a slight jiggle).

Cool and Chill:
Let the bars cool completely in the pan on a wire rack.
Once cooled, cover the pan and refrigerate for at least 2-4 hours, or until firm.

Serve:
Use the parchment paper overhang to lift the bars out of the pan.
Cut into bars and serve chilled.