Wash, dry and peel sweet potatoes. Dice into 1 inch pieces for even cooking.
Set a steamer basket in a large pot and fill with water up to the basket. Add diced sweet potatoes to the basket and bring water to a boil. Cover with a lid and reduce to a simmer. Steam for 15-20 minutes or until sweet potatoes are fork tender.
Transfer sweet potatoes to a large bowl or pot. Add milk, 2 tablespoons butter, maple syrup and salt to the sweet potatoes and mash thoroughly with a potato masher or an electric mixer.
Preheat the oven to 350 degrees. Spray an 8 x 8 pan with spray oil. Add sweet potatoes to the pan.
In a small bowl mix together pecans, 1 tablespoon melted butter, and brown sugar. Sprinkle pecan mixture over top of mashed sweet potatoes. Top the sweet potatoes with mini marshmallows.
Bake for 15-20; until marshmallows are lightly browned. Serve hot and enjoy!