Preheat your oven to 350°F.
Mix graham cracker crumbs, sugar, and melted butter until combined. The mixture should resemble wet sand.
Press the mixture firmly into the bottom and slightly along the sides of a 9-inch springform pan.
Bake the crust for 10 minutes, then allow to cool to room temperature.
In a large bowl, add the softened cream cheese and beat until smooth. Gradually mix in the sugar.
Mix in the pumpkin purée and sour cream until well combined.
Incorporate eggs individually, mixing on low speed after each addition until just combined.
Stir in vanilla extract, pumpkin pie spice, and flour until just mixed.
Pour the filling over the crust.
Cover the base of the pan with aluminum foil and set it inside a larger roasting pan. Add hot water to the roasting pan until it reaches halfway up the side of the springform pan.
Bake for 45-55 minutes or until the center is almost set.
Turn off the oven and crack the door open. Let the cheesecake sit in the oven for 1 hour.
Remove from oven and water bath. Cool to room temperature, then refrigerate for at least 6 hours or overnight.
Run a knife around the edge to loosen. Remove the pan's sides, slice, and enjoy. Serve with whipped cream if desired.