
Let the pie crust soften at room temperature until it is ready to roll.
On a lightly floured surface, roll the pie dough into a 13-inch circle, about ⅛-inch thick. Press the dough into a 9-inch deep-dish pie plate. Trim any uneven edges, leaving a 1-inch overhang. Tuck the overhang under and press the crust to the rim of the pie plate. Crimp the crust with your fingers or as you like. Place in the freezer for 20 minutes.
While the crust is chilling, preheat the oven to 425°F.
Press a piece of parchment paper inside the crust to fully cover it, then fill it with pie weights or dry baking beans. Bake for 10 to 12 minutes until the edges of the crust look dry.
Meanwhile, prepare an egg wash by whisking the egg with the heavy cream in a small bowl.
Remove the weights and paper. Brush all over the inside and edges of the crust with the egg wash. Poke the crust 10 to 12 times all over with the tines of a fork. Return to the oven for 6 to 8 more minutes until the inside looks dry and the crust is lightly golden. Let the crust cool while you make the filling.
Reduce the oven temperature to 350°F.
In a large bowl, whisk to combine the brown sugar, granulated sugar, cinnamon, pumpkin pie spice, and salt. Add the pumpkin puree, heavy cream, milk, eggs, bourbon or rum (if using) and orange zest. Whisk until smooth.
Pour the pumpkin mixture into the cooled crust. Cover just the crust with a pie shield made of foil. Bake for 55 to 60 minutes until the sides are set and the center is just barely wobbly. Let cool to room temperature, about 3 hours.
In a medium, heat-proof mixing bowl (that fits over a double-boiler), combine the egg whites, sugar, and cream of tartar. Whisk vigorously for about 1 minute, until the mixture is frothy.
Fill the double-boiler with 1-inch of water. Place it over medium-high heat and bring to a simmer. Reduce the heat to medium-low and place the bowl with the egg mixture over top. (Be sure that the base of the bowl does not touch the water.)
While stirring frequently with a silicone spatula, cook the egg mixture for 12 to 14 minutes until the sugar is dissolved and the temperature is between 165°F to 170°F on an instant-read thermometer.
Place the egg white mixture in the bowl of a stand mixer fitted with the whisk attachment. Add the vanilla and salt. Beat on medium-high speed (level 8) until thick and glossy and the sides of the bowl are barely warm to the touch, 8 to 10 minutes.
Dollop the meringue on top of the cooled pie. Use an offset spatula to spread the meringue to the edges of the pie crust and create swoops, swirls, and texture.
Use a kitchen torch to toast the meringue lightly all over. Slice and serve within 6 hours of topping the pie.