Ingredients
1 cup all-purpose flour, plus more for dusting
1/2 cup fine yellow cornmeal
1/2 teaspoon coarse salt
3 tablespoons sugar
1 stick chilled unsalted butter, cut into 1/2-inch pieces
1 large egg, separated
2 to 3 tablespoons ice water
2 1/2 pounds sweet potatoes (5 medium)
1 cup whole milk
3 tablespoons unsalted butter, melted
3 large eggs
1/3 cup sugar
1/2 teaspoon coarse salt
3/4 teaspoon ground cinnamon
1/8 teaspoon freshly grated nutmeg
1 teaspoon grated peeled fresh ginger (from a 2-inch piece)
Lightly sweetened whipped cream, for serving (optional)
Preparation
Crust: Preheat oven to 375 degrees, with racks in upper and lower thirds. Pulse flour, cornmeal, salt, and sugar in a food processor to combine. Add butter and pulse until pea-size clumps form. Whisk together egg yolk and 2 tablespoons ice water in a small bowl. Drizzle over flour mixture; pulse until mixture just begins to hold together when pinched. (If too dry, drizzle with another tablespoon ice water, and pulse a few more times.) Transfer dough to a piece of plastic wrap, loosely cover, and press into a disk. Refrigerate until firm, at least 30 minutes and up to 1 day.
Roll out dough to a 12-inch round on a lightly floured work surface. Transfer to a 9-inch pie dish. Trim edges, leaving a 1/2-inch overhang. Fold edge of dough under itself until flush with edge of dish.
Gather dough scraps, reroll, and stamp out various leaf shapes with cookie cutters. Transfer to a parchment-lined baking sheet. Whisk egg white with 1 teaspoon water in a small bowl; brush over cutouts. Refrigerate crust and cutouts until firm, about 30 minutes.
Line piecrust with parchment; fill with pie weights or beans. Bake on upper rack until bottom is dry, 20 to 25 minutes. Remove parchment and weights; return to oven. Place sheet with cutouts on lower rack; bake crust and cutouts until golden, 10 to 15 minutes. (If edges of crust are browning too quickly, tent with foil.) Let cool completely.
Filling: While crust is cooling, pierce potatoes with a fork; place on a parchment-lined rimmed baking sheet. Bake until very soft, 1 hour to 1 hour, 15 minutes. When cool enough to handle, scoop flesh from skins. Transfer 2 cups flesh to a food processor (reserving remainder for another use); puree with milk, butter, eggs, sugar, salt, cinnamon, nutmeg, and ginger until smooth.
Pour filling into piecrust; smooth top. Bake until edges are puffed slightly and center is set, 1 hour to 1 hour, 20 minutes. (If crust is browning too quickly, tent with foil.) Let cool completely. Top with leaf cutouts and serve, with whipped cream.
