Separate the eggs and reserve the egg whites in the refrigerator.
Whisk together the egg yolks and brown sugar in a medium sized heavy bottomed sauce pot. Whisk in the milk, gelatin, salt, and spices. Stir in the canned pumpkin so everything is thoroughly combined and there are no lumps.
Place pot over medium heat and cook, stirring constantly, until the mixture comes to just below a boil. DO NOT boil. The mixture should thicken. If using a thermometer, it should be done around 165 degrees Fahrenheit.
Remove from heat, cool slightly, and transfer the pumpkin mix to a bowl. Place the bowl in the refrigerator and allow to cool completely, stirring occasionally. The mixture should mound slightly when spooned. This part can be done in advance the day before. Make sure it is fully chilled before using.
To finish the pie filling, bring the egg whites to room temperature. Beat the egg whites with a hand mixer with whip attachment until soft peaks form. Slowly add the white sugar and beat the egg whites until stiff and glossy.
Place the chilled pumpkin custard in a large bowl and fold in the sour cream until combined. Fold in the whipped sugared egg whites. Spoon the chiffon mixture into the baked pie shell. Chill several hours before serving.
To serve, top each piece with lightly sweetened whipped cream.