Prepare the pastry dough: Sift together the flour and salt into a mixing bowl. Work the shortening into the flour with your fingertips or a pastry blender, until the mixture is the consistency of coarse meal. Add the water, 1 tablespoon at a time, and mix with a fork after each addition. Dough should not be wet, but just moist enough to hold together. Form the dough into a ball. Wrap and refrigerate for at least 15 to 30 minutes before rolling. Roll it out to line a 9-inch pie pan. Flute the edge of the shell. Set aside.

Preheat the oven to 425°F.

Mix the eggs, granulated sugar, and brown sugar together in a large bowl. Beat well until smooth and creamy. Add the sweet potato and mix thoroughly. Beat in all the milk, butter, and spices. Pour into the pie shell. If desired, sprinkle pecans on top of the filling.

Bake for 10 minutes. Reduce the heat to 350°F. and bake for 35 to 40 minutes more, or until a thin knife inserted into the pie comes out clean. Remove the pie from the oven and place on a rack to cool. Serve at room temperature or cold.