Place the sweet potatoes in a large pot. Add enough cold water to cover by 2 inches. Add a generous pint of salt and bring to a boil over medium-high heat. Cook until the potatoes are slightly soft but still hold their shape, 10 to 12 minutes. Strain and place back in the pot.
Combine the chicken broth and brown sugar in a 10-inch skillet over medium heat and cook until reduced by half, about 5 minutes. Add 3 tablespoons of butter, pumpkin pie spice, a generous pinch of salt and pepper, and stir to combine. Add the cooked sweet potatoes and gently toss to coat. Cook until the liquid has reduced down and is a syrupy consistency and the sweet potatoes are tender, about 5 minutes, making sure to stir every minute.
In a large bowl combine the corn cereal, pecans, maple syrup, and 2 tablespoons melted butter and stir until combined. Set aside.
Top the sweet potatoes with an even layer of marshmallows and let cook for 3 minutes to allow them to melt a bit. Top with the crunchy topping. Reduce heat to low and cook until marshmallows are completely melted, about 2 minutes.