Preheat the oven to 300 degrees F.
In the bowl of an electric mixer, combine the sweet potatoes and 1/2 cup of the sugar, as well as the eggs, butter, milk, vanilla, cinnamon, nutmeg and salt. Beat until thoroughly blended and smooth. Pour the mixture into the pie shell and sprinkle with the remaining 1/4 cup sugar. Allow the pie to stand for 15 minutes before baking to allow the sugar to melt.
Bake until a toothpick inserted in the center comes out clean, about 1 hour. Cool before serving.
Georgia Cooking in an Oklahoma Kitchen by Trisha Yearwood (c) Clarkson Potter 2008