Preheat oven to 400 degrees F and line a baking sheet with aluminum foil.

Scrub the sweet potatoes and pierce them on all sides using a fork. Place the sweet potatoes on the baking sheet.

Bake in the oven for about 45 minutes, or until potatoes are tender throughout.

In a small mixing bowl, combine the softened butter, brown sugar, chopped pecans, and ground cinnamon. Mix well with a fork.

Cut each sweet potato down the middle once tender and use a fork to mash the center slightly.

Spoon the butter mixture into each sweet potato and top with ¼ cup mini marshmallows.

Place the baking sheet back into the oven and broil for about 20 seconds, or until golden brown. Remove and serve.