If using a frozen crust or store-bought pie crust sheet, follow the instructions on the package for partially baking.

If using a homemade crust, preheat the oven to 400 F and place a baking sheet in the oven. Line the pie shells with foil. Fill the lined pie shells with pie weights, dried beans, or uncooked rice.

Bake the lined pie shells with weights for 15 minutes, until the edges of the crusts look dry and just begin to show signs of browning. Remove the crusts from the oven and remove the foil and weights. Return the crusts to the oven and bake for 7 minutes longer. Transfer the partially baked crusts to racks and aside while you make the filling. Reduce the oven temperature to 350 F.

If you don't par-bake the crusts, cook the pies at 425 F on the bottom oven rack for 10 minutes, and then reduce the oven temperature to 350 F and continue to bake for about 40 minutes or until set.

Combine the melted butter, mashed sweet potatoes, granulated sugar, milk or cream, and vanilla in a bowl. Blend with an immersion blender until very smooth. Alternatively, blend the filling mixture in an electric blender.

Blend in the eggs, cinnamon, ground nutmeg, and salt.

Pour the filling into the prepared pie shells and bake at 350 F for 55 to 65 minutes, or until the filling is set with just a slight jiggle in the center. Check on the pie after about 25 minutes for over-browning. Place pie shields or aluminum foil strips over the crust edge if necessary.

Transfer the baked pies to a rack and let them cool for 1 1/2 hours. Cover the cooled pies and store them in the refrigerator until serving time.