Prepare graham cracker crumbs by pulsing the crackers in a food processor, or placing the crackers in a zip-top bag and rolling over them with a rolling pin.
Make sure to let your cream cheese soften to room temperature before mixing the filling to avoid lumps.
1 Heat the oven to 350F. Spray a 9×13 baking pan with non-stick spray and line with parchment paper, allowing the edges to hang over the sides of the pan. This will help remove the bars for slicing and keep the crust intact.
2 Make the graham cracker crust: Combine all the ingredients for the graham cracker crust in a bowl. Stir the mixture together until it looks like wet sand. If it still looks dry, add an another tablespoon of melted butter. Transfer to the lined baking pan and press with your hand or the bottom of a drinking glass to form an even crust.
3 Make the streusel topping: In the same bowl used to make the graham cracker mixture, combine the ingredients for the streusel topping. Mix the ingredients together, using your hands if needed, to ensure the mixture comes together evenly. The mixture should resemble large crumbles. Set aside.
4 Make the pumpkin filling: In a stand mixer fitted with a paddle attachment, beat the cream cheese, sugar and vanilla until smooth. Stop the mixer and scrape down the sides of the bowl. Add the eggs, one at a time, mixing for 30 seconds in between. Scrape the bowl down again. Add in the pumpkin puree and pumpkin pie spice, and mix until completely combined.
5 Assemble the bars: Pour the pumpkin filling into the pan on top of the graham cracker crust. Smooth out evenly. Sprinkle the streusel topping over the pumpkin filling.
6 Bake the bars for 45 to 50 minutes: Check the bars at 40 minutes to see how quickly they are baking. When done, a toothpick inserted in the middle should come out cleanly.
7 Cool the bars completely and refrigerate: Let the bars cool to room temperature on a wire rack. Once cool, place in the fridge to chill completely.
Slice and serve with caramel sauce drizzled over the top and whipped cream, if desired. Bars will keep, refrigerated, for about a week.