Place cubed sweet potatoes in a medium saucepan and add water to cover. Bring to a boil, reduce heat to medium and cook 15 minutes, uncovered, until tender.
Preheat oven to 425 degrees F. Prepare a single pie crust in a pie pan and set aside.
Drain potatoes and return to pan. Mash until smooth, and allow to cool to room temperature. You should have about 2 cups mashed sweet potatoes.
In a large mixing bowl, cream butter and sugar together until smooth. Add eggs and mix well. Add (2 cups) mashed sweet potatoes, milk, vanilla, nutmeg, cinnamon and salt. Mix on medium speed until incorporated and smooth. Pour filling into pie crust.
Bake for 15 minutes, then reduce oven temperature to 350 degrees F. Continue baking for 30 to 40 minutes, until a knife inserted in center comes out clean. Cool completely and store in refrigerator until ready to eat.
Nutritional information is based on a standard pie crust. Depending on the brand of crust used, nutrition may vary.SERVING: Serve the pie with whipped cream or a scoop of ice cream, if desired.STORAGE: Let the pie cool and rest for at least 4 hours, however 24 hours or overnight is best.FREEZING: Allow the pie to cool completely. Wrap in plastic wrap and then aluminum foil. Freeze for up to 2 months. When you are ready to eat, make sure to thaw slowly in the refrigerator to avoid weeping.