In a medium bowl stir together the sugars, pumpkin pie spice, and cornstarch
In a large bowl beat the cream cheese until soft. Then beat in the sugar mixture.
Scrape down the sides of the bowl.
With the mixer on low beat in the sour cream, pumpkin puree & vanilla extract.
Mix in the eggs 1 at a time until just combined.
Pour the mixture into the prepared pan.
Bake for 40-45 minutes, or until theres just a slight wobble in the middle of the cheesecake.
Turn off the oven and open the oven door. Cool the cheesecake in the oven with the door open for 30 minutes.
Then remove from the oven and continue cooling to room temperature. Cover the pan, and chill in the fridge for at least 4 hours or overnight.
When ready to serve, use the aluminum foil to lift the cheesecake bars out of the pan and place on a cutting board.
Slice into pieces and serve with whipped cream.