Sweet Potato Casserole With Marshmallows

Preheat oven to 350° and grease a 9-x-13" baking dish with cooking spray. Place sweet potatoes in a large pot and cover with water. Bring to boil then reduce heat and simmer until the sweet potatoes are tender, about 15 minutes. Drain and let cool slightly then transfer to a large bowl. In a large bowl, stir together sweet potatoes, sugar, butter, vanilla, milk, eggs, and salt until smooth. Pour into prepared dish. In a medium bowl, stir together sugar, flour, and butter until it clumps. Stir in pecans, then spread evenly over potatoes. Top with marshmallows. Bake until cooked through and golden, about 30 minutes.