To make the crust, use a food processor to blend graham crackers into crumbs. Stir in the melted butter, ground nutmeg, and salt until combined. Press an even layer into the bottom of a 9-inch springform pan and refrigerate while you make the filling.
Preheat oven to 350°F. Using a stand mixer fitted with the paddle attachment, beat the softened cream cheese with the sour cream for a few minutes, until smooth. Add the pumpkin puree, powdered sugar, pumpkin pie spice, and vanilla extract and beat to combine.
Pour the filling onto the prepared crust and bake for 45-50 minutes. Cool completely, then cover and chill in the refrigerator for at least 1 hour (or until ready to serve).
Make sure to use blocks of cream cheese rather than the spreadable cream cheese that comes in a tub.
Do not use pumpkin pie filling -- make sure your canned pumpkin puree is 100% pure pumpkin with no added flavors.