Combine the graham style crumbs with ¼ cup sugar and the butter until well combined. Press firmly into the prepared pan and refrigerate while making the filling.
For the Filling & Topping:
Mix the water and gelatin in a small bowl and let sit for 5 minutes.
In a medium saucepan, combine ½ cup sugar, pumpkin puree, 3 egg yolks, milk, and pumpkin pie spice. Heat over medium heat, stirring frequently, until mixture is hot and thick, about 5 minutes. Do not let boil. Remove from heat, stir in the vanilla and gelatin, and let cool to room temperature. Do not refrigerate at this point.
Once the pumpkin mixture has cooled, beat the egg whites in a separate bowl until foamy with an electric mixer. Slowly add in ¼ cup sugar and beat until stiff peaks form. Stir a large dollop of the egg whites into the pumpkin mixture, then fold in the rest. Spoon the mixture into the pie crust, smooth the top, and refrigerate until set, at least 4 hours.
Before serving, whip the cream and powdered sugar until soft peaks form. Spread or pipe onto the pie, dust with some pumpkin pie spice, and serve.