Preheat your oven to 350°F (175°C). In a medium bowl, combine graham cracker crumbs, sugar, melted butter, and cinnamon if using. Mix until evenly moistened.
Press the mixture firmly into the bottom and slightly up the sides of a 9-inch springform pan. Use the flat bottom of a measuring cup to create an even, compact layer.
Bake the crust for 10 minutes until lightly golden. Remove from oven and allow to cool while preparing the filling. Reduce oven temperature to 325°F (163°C).
In a large bowl, beat the softened cream cheese and sugar until completely smooth – about 4 minutes on medium speed. Scrape down the sides and bottom of the bowl frequently.
Add the pumpkin puree, vanilla extract, and pumpkin pie spice to the cream cheese mixture. Beat on medium-low speed until just combined and uniform in color.
Add eggs one at a time, beating briefly after each addition just until incorporated. Then, stir in the heavy cream manually with a spatula.
Wrap the outside of your springform pan with a double layer of aluminum foil to prevent water from seeping in. Place the pan on a larger baking sheet for easier handling.
Pour the filling into the prepared crust, smoothing the top with a spatula.
Place the foil-wrapped springform pan inside a larger roasting pan. Fill the roasting pan with hot water to reach halfway up the sides of the springform pan.
Bake for 55-65 minutes until the edges are set but the center still has a slight jiggle (about a 2-3 inch wobbly center is perfect).
Turn off the oven, crack the door open slightly, and let the cheesecake cool inside for 1 hour.
Remove from the water bath, peel off the foil, and cool completely at room temperature. Refrigerate for at least 4 hours or overnight before serving.
Optional: Before serving, prepare whipped topping by beating heavy cream, powdered sugar, and vanilla until stiff peaks form. Pipe or spread onto the chilled cheesecake and dust with cinnamon.