Place the peeled sweet potatoes in a pot with 1/2 cup of cold water. Bring to a boil, cover, and reduce the heat. Simmer for 15-25 minutes or until sweet potatoes are tender enough to mash. Drain and transfer to a large bowl to cool slightly.

Preheat the oven to 375ºF. Spray a casserole dish with cooking spray.

Mash the sweet potatoes with a potato masher or two forks.

Add brown sugar, butter, vanilla extract, cinnamon, nutmeg, salt, and 1/4 cup of pecans to the mashed sweet potatoes. Mix until well combined.

Transfer the mixture into the casserole dish and smooth it out evenly using the back of a wooden spoon.

Sprinkle the remaining pecans and mini marshmallows over the sweet potato mixture.

Bake for 15 minutes or until marshmallows are toasted. Serve and enjoy.