For the crust: In a large bowl, mix together the salt and 2 cups of the flour until combined. Add the cold butter and, using your fingers, squeeze and rub the butter into the flour until it is almost fully incorporated and forms a shaggy dough, about 5 minutes. Add the remaining 1 cup flour and toss until just combined.

In a small bowl, whisk together the ice water and vinegar, then drizzle over the top of the dough. Use your hands to incorporate the liquid, gently kneading to form a dough. If the mixture is too dry, add more water a teaspoon at a time, until the mixture comes together.

Divide the dough into 2 equal pieces. Form them into balls, then place each ball in a 1-gallon zip-top plastic bag (do not seal). Using a rolling pin, slightly flatten each ball of dough into a disk (about ½ inch thick) to make rolling easier later. Seal the bags and place them in the refrigerator for at least 2 hours and up to overnight.

Roll one disk of pie dough into a 13-inch circle on a lightly floured surface. Transfer the dough to a 9-inch deep-dish pie plate. Tuck the edges of the crust under to be even with the edge of the pie plate and crimp the edges as desired. Thoroughly prick the bottom and sides of the dough with a fork and place the pie plate in the freezer for 30 minutes. Freeze the remaining pie crust for future use.

Preheat the oven to 400℉. Line the pie crust with parchment paper or foil, then fill with baking weights or dried beans. Bake until the edges of the crust are lightly golden brown, 18 to 20 minutes. Remove the pie weights and parchment paper and return to the oven. Bake until the entire crust is golden brown, 10 to 15 minutes longer. Place on a cooling rack and let cool completely, about 30 minutes.

For the filling: While the crust cools, start the filling. Add ¼ cup cold water to a small bowl. Sprinkle the gelatin over the water and let sit for 5 minutes.

In a medium saucepan, whisk together the egg yolks, milk, pumpkin pie spice, salt, and ¾ cup of the granulated sugar. Cook over medium heat, whisking constantly, until the mixture thickens slightly and coats the back of a spoon, about 5 minutes. Add the bloomed gelatin mixture, whisking until fully dissolved. Turn off the heat and whisk in the pumpkin puree and vanilla. Transfer to a large bowl and let cool to room temperature, about 45 minutes.

When the pumpkin custard is almost completely cooled, make the meringue. In a stand mixer fitted with the whisk attachment, whip the egg whites on medium speed until frothy, 1 minute. Gradually add the remaining ¼ cup granulated sugar, then increase the speed to high and beat until stiff peaks, about 3 minutes.

Stir about ¼ of the meringue into the pumpkin custard until well combined, then gently fold in the remaining meringue using a rubber spatula until no streaks remain. Transfer the pumpkin mixture to the baked pie crust, spreading into an even layer. Refrigerate until set, at least 4 hours and up to overnight.

For the whipped cream: In a stand mixer fitted with a whisk attachment, combine the heavy cream and powdered sugar. Mix on medium-high speed until stiff peaks form, about 2 minutes.

Transfer the whipped cream to a piping bag fitted with a large star tip. Pipe the whipped cream around the edges of the pie filling. Dust some pumpkin pie spice over the whipped cream, if desired. For the best presentation, add the whipped cream no more than 12 hours before serving.