Stir together graham cracker crumbs, melted butter, and granulated sugar until the texture of wet sand. Press firmly into the bottom of a 9-inch springform pan, going about 1 inch up the sides. Use the bottom of a measuring cup to pack it tight. Refrigerate while you make the filling.

Sprinkle gelatin over water in a small bowl. Let sit 5 minutes to bloom, then microwave for 15-20 seconds until liquid. Set aside to cool slightly - it should be warm but not hot.

In a clean bowl, whip cold heavy cream with an electric mixer on medium-high speed until stiff peaks form, about 3-4 minutes. Transfer to another bowl and refrigerate.

Beat room temperature cream cheese with powdered sugar, pumpkin puree, pumpkin pie spice, and vanilla until completely smooth and no lumps remain, scraping down the bowl twice, about 3 minutes.

With the mixer running on low, slowly drizzle in the warm gelatin mixture until incorporated. Remove bowl from mixer and fold in the whipped cream in two additions using a rubber spatula - gentle folding keeps the filling light and airy.

Pour filling over the chilled crust and smooth the top with an offset spatula. Refrigerate uncovered for at least 4 hours, preferably overnight, until completely firm. Run a thin knife around the edge before releasing the springform.