As the pie bakes, the filling separates into a silky, creamy custard base with a featherlight souffleed pumpkinlayer on top.
Preheat oven to 375 degrees with a rack in lower third. On a lightly floured work surface, roll out dough to a 13-inch round. Transfer to a 9-inch deep-dish pie dish. Using kitchen shears or a paring knife, trim dough to a 1-inch overhang. Fold overhang under itself to form a rim; pinch between thumb and forefinger to form a uniform edge around rim of dish. Crimp with fingertips. Refrigerate until firm, 30 minutes.
Blind-bake crust: Line dough with parchment. Fill with dried beans or pie weights; bake until crust is firm and dry, about 30 minutes. Carefully remove parchment and beans. Bake until light golden, about 5 minutes more. Transfer to a wire rack; let cool completely.
In a large bowl, whisk together pumpkin, 1/2 cup sugar, salt, spices, and vanilla until smooth. In a separate bowl, whisk egg yolks with remaining 1/2 cup sugar until thick and pale. Stir into pumpkin mixture just to combine; stir in milk and cream. With a handheld mixer or a stand mixer fitted with the whisk attachment, beat egg whites on low speed until foamy. Increase speed to medium-high and beat until stiff but not dry peaks form. Stir one-third of whites into pumpkin mixture. Gently fold in remaining egg whites until no streaks remain (do not overmix). Transfer to cooled crust and smooth top with a spatula.
Bake until puffed and golden brown on top and set at edges, but still slightly wobbly in center, 45 to 55 minutes (if pie is browning too quickly, tent edges of crust with foil). Transfer to wire rack; let cool completely. Refrigerate until cold, at least 1 hour or, loosely covered, up to 1 day. Serve, with whipped cream and a light dusting of nutmeg.