Make the Crust
Cut the butter into 1/2-inch-thick pieces. Lay the pieces in a single layer on a plate and put the plate in the freezer for 10 minutes.
Combine the all-purpose flour, whole-wheat pastry flour, sugar, and salt in the bowl of a stand mixer. Fit the mixer with the paddle attachment and mix on low speed to combine the ingredients. Remove the butter from the freezer, add it to the mixer bowl, and combine on low speed for about 1 to 2 minutes, until the mixture resembles coarse crumbs with some large chunks of butter remaining. Turn off the mixer and use your hands to check the size of the butter; if there are any pieces larger than a nickel, pinch them between your fingertips to flatten them. Add the water and combine on low speed until the dough comes together but is still slightly shaggy; do not mix it until the dough is smooth and homogenous, like cookie dough.
The more you mix pie dough, the tougher the crust will be because you develop more gluten. And, when you overmix the dough, the chunks of butter break up; those chunks are what create the nice layers in a crust.
Put the dough on your work surface. Lay two long sheets of plastic wrap in a crisscross formation on your work surface. Place the dough in the center, where the two sheets cross. Use your hands to pat the dough into a round disk. Loosely wrap the dough in the plastic, leaving a few inches of slack all around. Run a rolling pin over each package of wrapped dough to roll it out in the plastic to a round or block. Place the dough in the refrigerator to chill for at least 2 hours and up to 2 days; or freeze it for up to 1 month.
Remove the dough from the refrigerator and set it on the work surface to rest for 10 to 15 minutes, until it is pliable but not soft.
Grease the bottom and sides of Sweetie Pie with butter.
Roll out the crust and line Sweetie Pie
Lightly dust a large flat work surface with flour. Unwrap the round of dough and place it on the floured surface. Lightly dust the dough and the rolling pin with flour and roll the dough out to a 1/8-inch circle (at least 15 inches in diameter), rotating the dough and dusting the work surface, dough, and rolling pin with flour as needed to prevent the dough from sticking to the work surface as you roll.
Gently fold the dough in half, pick it up, and place it on the pie plate with the fold running down the center of Sweetie Pie. Unfold the dough and adjust it so the circle of dough is centered over the plate. Use your hands to guide the dough into the bottom crease and up the sides of the plate. Using kitchen shears, trim the dough so it hangs over the edge of the pie plate by 1 inch all around. Tightly roll the overhanging dough toward the center of the pie plate to create a lip that rests on the ridge of the plate. Crimp the crust. Put the pie shell in the refrigerator while you make the filling and up to overnight. (If you are refrigerating the pie shell overnight, cover it with plastic wrap before refrigerating.)
Blind bake the crust
Arrange the oven racks so one is in the center position. Preheat the oven to 375 degrees Fahrenheit.
Remove the pie shell from the refrigerator. Cut a piece of parchment paper that is larger than the pie and lay it on top of the crust. Using your fingers, press on the paper to line the crust, working it into the crease and making sure it fits snugly against the sides all the way to the crimped edge. Fill the pie with pie weights or dried beans.
Put the pie shell on the center rack of the oven to bake for 40 to 50 minutes, until the edges are light golden brown and dry looking, and the shell is beginning to brown, rotating the pie shell from front to back halfway through the baking time so it browns evenly. Remove the pie crust from the oven and place it on a cooling rack to cool to room temperature with the pie weights or beans in place. Gently lift the edges of the parchment paper to remove the paper and weights. Put the weights or beans in a container to use the next time you need pie weights. (If you used dried beans, be sure to label them as pie weights before returning them to your pantry, so you don’t try to cook them.)
Make the filling
Peel the sweet potatoes and cut them into 1-inch pieces. Put the sweet potatoes in a pot fitted with a steamer insert, fill the pot with enough water so it comes just below the insert, and bring the water to a boil over high heat. Cover and steam the sweet potatoes until they are very tender when pierced with the tip of a knife. Turn off the heat, uncover the pot, and set the sweet potatoes aside to cool for about 5 minutes, until they are cool enough to handle.
Reduce the oven temperature to 325 degrees Fahrenheit.
Mix the filling
Transfer the sweet potatoes to the bowl of a food processor fitted with a metal blade and process until smooth. Add the butter, brown sugar, orange zest, salt, cinnamon, ginger, and nutmeg, and process until the additions are mixed in and the butter has melted. Transfer the pie filling to a large bowl, using a rubber spatula to get all of the filling out of the food processor bowl. Add the orange juice and then the evaporated milk, stirring with a whisk to combine. Set the filling aside to cool to room temperature, 30 to 40 minutes. Then whisk in the egg yolks.
Place the egg whites in the bowl of a stand mixer. Fit the mixer with the whisk attachment and whisk the whites on medium-high speed until they hold a peak, 4 to 5 minutes. Add the whites to the bowl with the sweet potato mixture and use the spatula to gently fold them into the filling. Pour enough filling into the prepared pie crust to come to the bottom of the crimped edge; pour any remaining filling into small ramekins or a small baking dish to bake and snack on. Use a small offset spatula to smooth out the filling.
Bake the pie
Line Holy Sheet with parchment paper.
Place the pie on Holy Sheet and put it on the center rack of the oven to bake for approximately 40 minutes, rotating the baking sheet from front to back halfway through the baking time, until the filling has puffed up and the custard is set; it will jiggle, but firmly, when you wiggle the pie. Remove the pie from the oven and set it on a cooling rack to cool to room temperature before serving.
Excerpted from A GOOD BAKE: The Art and Science of Making Perfect Pastries, Cakes, Cookies, Pies, and Breads at Home by Melissa Weller with Carolynn Carreño. Copyright © 2020 by Melissa Weller. Excerpted by permission of Alfred A. Knopf, a division of Penguin Random House LLC. All rights reserved.