Crust

1. Preheat the oven to 350F/180C. Line a 9-inch square pan with heavy-duty aluminum foil so that the foil overhangs on the sides, this will make it easier to remove the cheesecake bars from the pan after they have cooled and chilled. Grease the foil with non-stick spray and set aside.  
2. Use a food processor to pulse the graham crackers into crumbs or place them in a plastic bag and crush with a rolling pin into fine crumbs. In a small bowl combine graham crumbs and butter, until a sand-like texture is reached and all the crumbs are evenly moistened. Press into the bottom and slightly up upsides of prepared pan. Bake for 6 minutes then set aside while you prepare the filling. Reduce the oven temperature to 325F/ 163C. 

Pumpkin Cheesecake

1. In the bowl of an electric mixer fitted with a paddle attachment or large bowl with an electric mixer beat cream cheese for 2 minutes on low-medium speed. Make sure to scrape down the sides of the bowl, the cream cheese should be smooth with no lumps.
2. Mix in granulated sugar for a minute or two, again scraping down the sides of the bowl, this will really loosen the cream cheese. Next add the pumpkin puree, pumpkin pie spice, vanilla, and sour cream. Beat for another 2-3 minutes on low-medium speed.  You want to make sure everything is fully combined and there are no white spots. You should have a creamy batter with no lumps. Add in the eggs one at a time, making sure there are no traces of yolk left behind.
3. Pour batter into prepared pan. Place the 9-inch pan in a larger pan you can use whatever you have on hand, you just want it to sit into the pan with a little room around the sides so you can pour hot water into the larger pan to bake the cheesecake bars in a water bath. 
4. Bake for 45 minutes to 1 hour the middle of the cheesecake should jiggle just a little bit, the sides should be fully set. You can use a digital internal thermometer to check the cheesecake has reached 145F/63C. Turn the oven off, open the door and let cool in the oven for 45 minutes then take out of the water bath and let cool on a wire rack on the counter for an hour before wrapping with plastic wrap then chill in the fridge for at least three hours.
5. When chilled and ready to serve gently remove the foil and use a large knife to slice into bars. If desired pipe stabilized whipped cream on top and add a sprinkling of pumpkin pie spice. Store in the fridge in an air-tight container for up to 4 days.