Step 1

Preheat oven to 325°. Pulse graham crackers in a food processor until broken down into fine crumbs (you should have about 2 cups). Set aside 2 Tbsp. graham cracker crumbs for serving. Add sugar and salt and pulse just to combine. Add butter and pulse until mixture is the consistency of wet sand.

Step 2

Transfer to a 9½"-diameter deep pie dish. Using a measuring cup, press crumbs firmly onto bottom and up sides of dish. Bake crust until fragrant and edges just start to take on color, 20–25 minutes. Transfer to a wire rack and let cool.

Step 3

Stir gelatin, cinnamon, nutmeg, a scant ½ cup sugar, and ½ tsp. salt in a small saucepan. Whisk egg yolks and milk in a small bowl to combine, then whisk into sugar mixture. Cook over medium heat, stirring frequently, until mixture begins to thicken and coats the back of a spoon (but do not let it boil), about 5 minutes. Stir in pumpkin purée and remove from heat. Transfer to a large bowl and chill until cool, about 10 minutes.

Step 4

Meanwhile, using an electric mixer on medium-high speed, beat egg whites in a large bowl until soft peaks form. With the motor running, gradually add a scant ¼ cup sugar and continue to beat until stiff peaks form, 5–7 minutes.

Step 5

Mix one-third of egg white mixture into chilled pumpkin mixture until smooth. Gently fold remaining egg white mixture into pumpkin mixture in 2 additions until incorporated, but don’t overmix.

Step 6

Pour filling into graham cracker crust; smooth top. Cover and chill overnight.

Step 7

Vigorously whisk cream in a large bowl until medium peaks form. Fold in sour cream and remaining 2 Tbsp. sugar and ¼ tsp. salt just to combine. If the cream looks like it could use another whisk or two to hold medium peaks, give it a whisk until it reaches the desired consistency. Using a large spoon, dollop a generous amount of whipped cream in the center of pie. Sprinkle with reserved graham cracker crumbs. Slice and serve with any remaining whipped cream alongside.