Method
Preparation
Preheat the oven to 350°F (175°C).
Boil the sweet potatoes in a large pot of water until tender, about 20 minutes.
Drain the sweet potatoes in a colander and allow them to cool briefly, then peel them with a vegetable peeler or knife.
In a large bowl, mash the sweet potatoes with a potato masher or electric mixer until smooth.
Gently mix in the sugar, milk, softened butter, eggs, vanilla extract, and salt until the mixture is uniform and creamy.
Baking
Pour the sweet potato mixture into a greased baking dish and spread it evenly with a spatula.
Carefully top the casserole with mini marshmallows and sprinkle chopped pecans over the marshmallows if using.
Bake for 25-30 minutes, or until the top is golden brown and the edges are bubbly.
Allow the casserole to rest for a few minutes on a cooling rack before serving.
Notes
For freezing, you can freeze the baked casserole (without marshmallows) in an airtight container for up to 2 months. Use a mixer for extra-smooth texture. If using pecans, toast them in a dry skillet before sprinkling on top.