1) The crust: Pulse the flour and salt together in food processor. Scatter frozen butter over the flour; pulse until the mixture is the size of large peas, (about 20 pulses). Add Sour Cream, and pulse until the dough forms a ball. Flatten the dough into a 4" disk, wrap tightly in plastic, and chill for 1 hour, or up to 2 days (or freeze up to 1 month).
2) Preheat oven to 350 degrees. Let dough rest on the counter for 10 minutes to soften slightly. On a lightly floured work surface, roll dough into a 12" circle. Transfer to a glass pie plate. Trim excess dough, leaving about 1/2" hanging over the edge. Tuck excess underneathe itself to form a neat edge. Press in a decorative border with your fingers.
3) Line Pie Shell with a double layer of foil; fill with pie weights or old beans. Bake 15 minutes. Remove weights and foil, and continue baking until the crust is golden and crisp. (About 5-10 minutes more) Place Pie Shell on cooling rack.
4) Combine all the ingredients for the 'SPICE MIXTURE' mentioned in ingredience.
5) Pumpkin Custard: Whisk heavy cream, eggs, brandy, and 1 tsp of 'spice mixture'. Add the pumpkin and sugars, whisking to combine. Pour Pumpkin Custard into warm pie crust. Bake until the edges are set and the center registers 175 degrees on instant thermometer -- about 30 minutes. Cool to room temperature (about 1 - 2 hours).
6) Pumpkin Chiffon: Combine the gelatin and 1/4 cup cold water in a small saucepan and let soak for 5 minutes (to firm up a bit).
7) In a saucepan at medium heat, whisk together the Pumpkin Puree, Brown Sugar, Egg Yolks, and 2 teaspoons of 'Spice Mixture'. Stirring constantly, bring to a simmer. Remove from heat and transfer into a bowl.
8) Heat the Gelatin in the saucepan over low heat until melted, 1 - 2 minutes. Stir the Gelatin into the chiffon until well combined. Chill covered until the mixture is just set (about 15 - 20 minutes) and the center jiggles slightly when shaken.
9) Using and electric mixer, whip the egg whites at medium-low speed until frothy (about 1 - 2 minutes). With the mixer still running, sprinkle in 2 tbls. Sugar, and increase the mixer speed to medium-high, whipping until stiff peaks form (about 1 -2 minutes).
(If you are concerned about the use of raw egg whites, you can whisk the egg whites and sugar in the top of a double boiler until the egg whites reach 140 degrees - just be careful that you don't end up with scrambled eggs - before beating them to stiff peaks).
10) Whisk a quarter of the Meringue into the Chiffon mixture to lighten it. Gently place the remaining Meringue on top of the chiffon, while you whip the heavy cream and 3 Tbls. of sugar into stiff peaks.
11) Gently fold the remaining Meringue and 1/4 cup of the whipped cream into the chiffon until no white streaks remain. Spread the chiffon mixture over the Pumpkin Custard, mounding it slightly higher in the middle. Spread the whipped cream attractively over the top, sprinkle with additional spices if desired.