Make the dough. In a large bowl, place the Gluten-Free All-Purpose Flour (4 cup), Baking Powder (3/4 teaspoon), and Kosher Salt (3/4 teaspoon). Whisk to combine well.
Add the Unsalted Butter (16 tablespoon) to the flour mixture. Toss to coat it in the dry ingredients. Flatten each chunk of butter between your thumb and forefinger so that it's about an 1/8-inch thick.
Create a well in the center of the dry ingredients and slowly add the ice cold Water (1 1/3 cup), mixing gently until the dough begins to come together. Press together with floured hands, press together the dough into a disk. If there are any crumbly, dry spots at this point, add more water by the teaspoonful and press together with your hands.
Begin to shape the dough. Turn out the dough onto a lightly floured surface. Sprinkle the top lightly with more flour, and roll out into a rough rectangle that is about 1-inch thick.
Sprinkle the dough lightly with more flour, fold it over on itself in thirds like you would a business letter, sprinkle again with flour, and roll out the dough once again into a rectangle about 1-inch thick. Repeat the process of rolling, sprinkling and folding at least once more, this time ending with a rectangle about a 1/2-inch thick.
Using a pizza wheel, pastry cutter or sharp knife, slice the rectangle in half along the length, creating two rectangles of equal size, and roll each separately in thirds once more. Wrap each piece of dough securely in plastic wrap, and place in the refrigerator to chill until firm (30 minutes to an hour).
Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 9x13-inch baking dish with soft Butter (to taste).
In a large bowl, whisk the Egg (6), Granulated Sugar (1 cup) and Dark Brown Sugar (1/2 cup) to combine. Whisk in the Heavy Cream (1 cup), then the Canned Pumpkin Purée (30 ounce) and Pure Vanilla Extract (2 teaspoon). Add the Ground Cinnamon (1 tablespoon), Ground Ginger (2 teaspoon), Ground Allspice (1 teaspoon), Ground Nutmeg (1/2 teaspoon) and Fine Sea Salt (1/2 teaspoon) and whisk to combine.
Pour the custard into the prepared casserole dish. Partially bake for 20 minutes. Remove dish from oven and allow to slightly cool.
Finish shaping the crust. Once the dough has chilled, remove one piece from the refrigerator, unwrap it and place it on a lightly floured surface. (Reserve remaining dough for another time.) Sprinkle the top lightly with more flour, and on a lightly floured surface, roll out the dough to about 1/4-inch thick. Using a scalloped-edge round cutter, form as many dough discs as possible.
Gently lay the dough discs all over the partially baked pumpkin custard, in a slightly overlapping pattern. Egg wash the surface of the pie dough, and sprinkle evenly all over with Raw Sugar (to taste). Return to the oven and bake until the pie crust is deeply golden brown, 25 to 30 minutes.
Serve warm or cool to room temperature. Delicious when served with a side of freshly whipped cream.