Preheat your oven to 350°F (175°C).
Peel and chop sweet potatoes into large chunks.
Boil sweet potatoes until fork-tender, about 20 minutes.
Drain and return sweet potatoes to the pot.
Add melted butter, brown sugar, milk, eggs, vanilla, cinnamon, and nutmeg to the sweet potatoes.
Mash the mixture until smooth and well combined.
Transfer the mixture to a greased casserole dish.
Sprinkle with mini marshmallows and chopped pecans on top.
Bake in the preheated oven for 30-35 minutes, until marshmallows are golden.
Let the casserole cool for a few minutes before serving.
