3 medium sweet potatoes (about 1½ pounds, for 2½ cups cooked and mashed)
1 (9-inch) unbaked deep-dish pie crust
1 cup brown sugar, firmly packed
1 stick (½ cup) butter, softened
1 teaspoon ground cinnamon
¾ teaspoon ground ginger
½ teaspoon ground nutmeg
2 large eggs
½ cup evaporated milk
¼ cup sugar
Whipped cream, optional for serving
Place the raw sweet potatoes in a 4½-quart (or larger) pot. Cover the potatoes with tap water. Place the pot over high heat, and bring it to a boil. Cook at a moderate boil (lower the heat, if necessary, to prevent splatters), until the potatoes are very tender when pierced with a small sharp knife, about 35 minutes. Use tongs to remove the potatoes from the water, and allow them to cool, or refrigerate until ready to use. (See note if you plan to refrigerate the potatoes.)
Prepare the pie crust in a deep-dish pie plate, and set it aside. Heat the oven to 400 degrees.
Peel the potatoes (the jackets usually slip right off), and lightly mash the flesh. Use 2½ cups potatoes. (Reserve any extra for another use.)
In the large bowl of an electric mixer, combine potatoes, brown sugar, butter, cinnamon, ginger and nutmeg. Mix on medium speed until light and fluffy, about 2 minutes.
Meanwhile, separate the eggs, placing the egg whites in the small bowl of an electric mixer. Set aside. Add the yolks to the potato mixture, and mix well. Add the evaporated milk, and mix just until well blended.
Beat the egg whites, adding 1 tablespoon sugar at a time, until stiff peaks form, about 3 minutes. (See note.)
Fold the egg whites into the potato mixture. Spoon the mixture into the prepared pie shell. (Mound the mixture in the middle, taking care not to let the filling spill over the edge of the crust, as there will be a significant amount.) Bake at 400 degrees 10 minutes; then reduce the heat to 350 degrees. Continue to bake 45-55 minutes. When the pie is done, the center will be just set and will jiggle only slightly.
Remove from the oven, and let the pie cool 20-30 minutes before slicing. Serve with whipped cream, if desired. Refrigerate any leftovers.
Cook's note: If you precook the potatoes, warm them slightly in the microwave before blending with the softened butter for a smoother finished pie. For testing purposes, I used Pillsbury Refrigerated Pie Crust. Beat the egg whites at room temperature.
Nutrition values per serving: 305 calories, 15 g fat (9 g saturated), 40 g carbohydrates, 2 g fiber, 4 g protein, 82 mg cholesterol, 143 mg sodium.