If you like sweet potato casserole, you’ll love this delicious pie. Creamy sweet potato custard is baked inside a piecrust and then topped with a marshmallow-like toasted meringue topping. It’s the perfect way to end any fall meal.
Put the flour, ¼ teaspoon of the salt, and 2 teaspoons of sugar into the bowl of a food processor and pulse a few times until mixed. Add the butter and shortening and pulse a few more times until the pieces of fat are about the size of peas. Add the water, a few tablespoons at a time, pulsing the dough just until it starts to look crumbly and slightly hydrated.
Take a handful of dough and squeeze it. If it holds its shape, shape it into a disc, wrap it in plastic wrap, and chill it in the refrigerator for an hour. If it doesn’t hold it’s shape, a few more tablespoons of water and pulse in the food processor until it does.
Meanwhile, heat the oven to 450 degrees. Wash and dry the sweet potatoes. Using a fork, poke holes all over the potatoes, place them on a sheet pan and then roast them in the oven until they are soft, about 45 minutes to an hour. Let them cool completely on the sheet pan before peeling and mashing them.
While the potatoes are cooling, roll the pie dough into a large disc, line a pie pan with the dough, and crimp the edges. Put the pie pan into the refrigerator and allow the piecrust to cool until you are ready to use it.
When you’re ready to bake the pie, preheat the oven to 350 degrees F.
Combine 2 cups of mashed, cooked sweet potato, ½ cup of the granulated sugar, the brown sugar, eggs, vanilla, cinnamon, and cream. Mix thoroughly. Slowly stream in the melted butter, whisking to combine.
When the filling is combined, pour it into the chilled piecrust and bake it in the oven until the center of the custard is just set, about 1 hour. Allow the pie to cool.
When the pie has reached room temperature, whisk the egg whites with an electric mixer, adding the last ¼ cup of granulated sugar about a tablespoon at a time until the egg whites form a thick, glossy meringue. Top the pie with the meringue and then put the pie in a 250-degree oven until the meringue is toasted and slightly browned, about 15 minutes.