Prepare the sweet potatoes by peeling and cutting them into chunks. Boil in water for 15-20 minutes until tender, then mash until smooth.

If using a pre-made pie crust, skip this step. For homemade, mix flour, butter, and salt, add cold water, roll out, and bake for 10 minutes at 350°F.

In a mixing bowl, combine mashed sweet potatoes, sugar, milk, melted butter, eggs, vanilla, cinnamon, nutmeg, and salt. Mix until smooth.

Prepare the meringue by beating egg whites and cream of tartar until soft peaks form. Gradually add sugar and beat until stiff peaks form.

Assemble the pie by pouring sweet potato filling into the crust, topping with marshmallows, and spreading meringue over the top.

Bake the assembled pie at 350°F for 10-15 minutes until the meringue is golden brown. Cool for at least 1 hour before serving.