Fill a large saucepan halfway with water and bring to a boil over high heat. Add Sweet Potato (5 pound) and boil for 20 minutes, or until a fork easily goes through the centers of the potatoes. Drain and mash.
Preheat oven to 350 degrees F (180 degrees C) and coat a 9x13 pan with cooking spray. Set aside.
Add the Egg (2), Butter (1 stick), Milk (1/2 cup), Brown Sugar (1/2 cup) and Pumpkin Pie Spice (1 teaspoon) to the mashed potatoes. Mix well and pour into prepared baking dish, spreading into an even layer.
In a medium bowl, combine the Brown Sugar (1/2 cup), All-Purpose Flour (1/2 cup), Pecans (1 cup), and Butter (1/2 stick). Mix and pour evenly over sweet potatoes. Bake in the preheated oven for 20 minutes.
Add the Mini Marshmallows (5 cup) on top and bake for another 5 minutes.