Step 1

Wash the whole sweet potatoes and drain them.

Step 2

Place the sweet potatoes in a large pot and add cold water to cover by 2 inches.  Bring the water to a boil over medium heat, and cook until the potatoes are tender, 30 to 40 minutes.  (A fork should pierce the potatoes easily but they should not fall apart.) When the potatoes are done, drain and cool them.

Step 3

Preheat the oven to 375 degrees F.  Prepare the pastry for a 9-inch single-crust pie.

Step 4

When the potatoes are cool enough to handle, peel and mash them in a large bowl with a hand mixer or a stand mixer.

Step 5

Add the melted butter, corn syrup, and sugar. Beat on medium speed. Discard the long, stringy fibers that collect around the electric beaters as you beat the filling. In the end, you want a smooth, string-free filling.

Step 6

Add the eggs one at a time. Beat well after each addition.

Step 7

Pour in the buttermilk.  Add the nutmeg, cinnamon, allspice, vanilla extract, and salt. Beat until the filling is smooth.  Pour the filling into the prepared pie crust.

Step 8

Bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean.  Remove from the oven and cool completely on a wire rack.  Garnish with whipped cream and serve it up.