1 teaspoon unflavored gelatin (from a 1/4-ounce envelope)
1 1/2 cups heavy cream
1/4 cup granulated sugar
Preheat oven to 400 degrees. Press a sheet of aluminum foil onto crust, draping over rim of pie plate. To blind-bake: Fill with dried beans or pie weights. Bake until edge of crust is firm, about 20 minutes. Remove beans and foil; let crust cool completely, and set aside.
Reduce heat to 350 degrees. Make filling: In a medium bowl, whisk together pumpkin, eggs, sugar, cinnamon, pie spice, vanilla, and salt; whisk in cream. Pour mixture into cooled crust; place pie plate on a rimmed baking sheet. Bake until filling is set, about 1 hour. Let cool on a wire rack, 1 hour; refrigerate to cool completely, about 2 hours.
Make topping: Place 3 tablespoons cold water in a small saucepan; sprinkle with gelatin, and let soften, about 5 minutes. Place pan over very low heat; stir until gelatin dissolves. Let cool slightly. In a large bowl, using an electric mixer, beat cream and sugar until very soft peaks form. While beating, slowly add gelatin mixture; continue to beat until soft peaks form.
With a rubber spatula, mound topping in center of chilled pie. Refrigerate at least 1 hour more (or up to 1 day). Sprinkle with more cinnamon before serving.
NOTE: Double the recipe to get enough filling for roughly 20 little mason jars. Fill the jars, stopping about 3/4" from the top. Bake at the usual temperature, but start watching them carefully after about 25 minutes since they won't take as long to bake as a pie. Pull them out when the center seems set (mine took about 35 minutes). Let cool for an hour or so, then throw them in the fridge while you make the whipped cream.