Buttermilk Sweet Potato Pie

On a lightly floured surface, roll out the dough on a lightly floured surface to 1/4 inch thick.
Roll the dough onto the rolling pin and gently transfer to the pie plate, unfurling the dough off the pin and into the plate. Trim the dough to have a 1/2 inch overhang all the way around the edges.
Tuck the excess dough under at the edges, working all the way around and pressing lightly to help the dough "seal" to the outer edge of the pie plate. Crimp the edges as desired (or use a fork). Return the dough to the refrigerator for 15-30 minutes.
While the crust chills, preheat the oven to 425 degrees Fahrenheit. Cut a square of parchment paper a little large than the pie plate. When the dough is chilled, pierce the bottom a few times with a fork. Place the parchment in the center of the pie and fill with pie weights. Bake until the crust is just barely golden brown, 10-12 minutes. Reduce the oven temperature to 375.
Remove the parchment paper and pie weights and brush the base of the pie crust with egg white. Return to the oven and bake for 3-5 minutes more. Cool the crust completely.
Make the filling: in a large bowl, whisk the sweet potatoes, butter, buttermilk, eggs, egg yolk, and vanilla to combine. Add the sugar, brown sugar, cinnamon, ginger, allspice, and nutmeg.
Pour the custard into the cooled crust. Bake until the custard is set around the edges but still slightly jiggly in the center, 35-40 minutes. Cool completely before slicing and serving.