Preheat the oven to 350°F (175°C).
Boil sweet potatoes until tender, then mash until smooth.
In a large bowl, combine mashed sweet potatoes and sugar.
Add milk, heavy cream, eggs, and vanilla extract, mixing well.
Incorporate cinnamon, nutmeg, and salt into the mixture.
Pour the filling into the prepared pie crust.
Bake in the preheated oven for 45-50 minutes, or until set.
Remove from oven and let cool on a wire rack.
Chill in the refrigerator before serving for best flavor.
Serve with whipped cream or vanilla ice cream, if desired.