- Bloom the gelatin by placing it in a bowl. Sprinkle the gelatin with the water and set aside for 5 to 8 minutes. 
- Meanwhile, place ¼ cup sugar, milk, spices, and salt in a saucepan. Cook over medium-high heat until the mixture barely comes to a simmer. 
- While the milk mixture is cooking, whisk together the egg yolks and remaining ¼ cup of sugar. Once hot, temper the milk mixture into the egg mixture by slowly whisking in a little of the hot milk in at a time. 
- Pour the egg-milk mixture back into the saucepan. Whisk in the pumpkin. Place the saucepan back on the stove over medium-low heat. Add the bloomed gelatin. 
- Stirring slowly yet constantly, bring the mixture to a slow boil (large bubbles will begin to “plop” on the surface). Continue whisking for another minute or 2 (or 160 degrees F) until thick and smooth. 
- Strain the pumpkin custard into a heat-safe container. Press a piece of plastic wrap directly on the top of the custard. Chill it in the refrigerator until completely cool. 
- After the custard cools, whip the 1 cup of cream. Begin mixing on medium-low speed until the cream begins to thicken slightly. Add the sugar and continue mixing on medium-high until soft peaks. Add the vanilla and mix until combined. 
- Fold the whipped cream into the cooled pumpkin custard. Start by stirring about ⅓ of the whipped cream into the pumpkin custard (no need to be gently here). Once the pumpkin custard is slightly lightened, fold in the remaining whipped cream. 
- Spoon the pumpkin chiffon filling into the pre-baked pie crust. Smooth it out with the back of a spoon or offset spatula. Return the pie back to the refrigerator to set, at least an hour or 2. 
- Top with a mound of fluffy whipped cream (or dollop small amounts on each slice when serving) and dust with cinnamon.