Scrub sweet potatoes under water to remove any excess dirt.
Place sweet potatoes in a large pot with water. Boil unpeeled sweet potatoes until tender (You should be able to stick a fork easily through the sweet potatoes.)
Let sweet potatoes cool then peel. Place sweet potatoes in a stand mixer bowl
Preheat the oven to 350 degrees.
With the whisk attachment whipped sweet potatoes for 3-5 minutes or until smooth.
Add granulated sugar and butter. Mix until sugar and butter are incorporated.
In a separate bowl, whisk together eggs, milk, and vanilla extract.
Add egg mixture to the sweet potatoes mixture and mix until combined.
Mix in cinnamon and nutmeg by hand.
Grab pie shells from the freezer and divide the sweet potato filling between both pie shells.
Optional: Cover exposed pie crust with aluminum foil to prevent burning.
Bake for 45 minutes to 60 minutes or until a toothpick placed in the center comes out clean.
Let pies cool then slice and serve with marshmallow topping or whipped cream.