The R&B legend's sweet potato pie is famous for a reason!
For the crust, in a bowl, whisk 1 1/2 cups flour and the salt. Using a pastry blender or your fingertips, mix in the shortening until the largest pieces of shortening are the size of a pea. Gradually add 1/4 cup ice water, stirring with a fork until moist clumps form. (If the dough is still dry, stir in more ice water by the teaspoonful.) Gather the dough into a ball and flatten into a disk. Wrap the dough in plastic. Refrigerate until slightly firm, 30 minutes to 1 hour.
On a lightly floured surface, roll the dough out to a 12- to 13-inch round, about 1/8 inch thick. Transfer to a 9-inch pie dish. Trim the edges, leaving a 1/2-inch overhang. Fold the edge of the dough over and crimp decoratively. Using a fork, pierce the dough all over. Freeze until firm, about 20 minutes.
Preheat the oven to 375°. Line the crust with foil; fill with pie weights, dried beans, or rice. Place on a large rimmed baking sheet. Bake until the edges of the crust are golden, 15 to 20 minutes. Remove the foil and weights. Continue baking until the crust begins to turn golden, 10 to 15 minutes more; pierce with a fork if it puffs up. Let cool.
For the filling, pierce each yam a few times with a fork. Microwave on high for 4 minutes; turn over and cook until tender, about 4 minutes more. Hold the yams in a kitchen towel; cut in half and scoop the flesh into a medium bowl. (You should have about 2 cups.) Using an electric mixer on medium speed, beat the yams and butter. Add the sugar, evaporated milk, eggs, spices, and salt. Beat until the sugar dissolves, 2 to 3 minutes. Scrape the filling into the crust and spread out evenly.
Bake the pie for 15 minutes. Reduce the temperature to 350° and continue baking until the center of the pie is set, 30 to 35 minutes more. Let cool on a wire rack for at least 1 hour.
For the whipped cream, place the cream, confectioners’ sugar, and vanilla in a cold bowl. Using an electric mixer, beat until soft peaks form. Serve with the pie.