1. Preheat oven to 375°F.

2. Mash sweet potatoes. Add butter, milk, cinnamon, brown sugar and salt to the potatoes and mash until smooth.

3. Transfer the mashed potatoes to casserole dish. Heat casserole dish with sweet potato mixture until warm.

4. While the sweet For the topping, in a medium bowl, combine butter, brown sugar, flour, cinnamon, salt, and pecans, and stir to combine.

5. Take sweet potatoes out of oven and top with half the marshmallows, then the streusel, then more marshmallows.

6. Place back into the oven for 10 minutes, until the the marshmallows begin to brown, be careful not to burn the marshmallows. Serve.