Preheat oven to 350 degrees F. Spray a 9x13 baking dish with cooking spray.
In a large bowl mix together the sweet potatoes, butter, white and brown sugars, eggs, milk, and cinnamon.
Spread the sweet potato mixture evenly into a prepared 9 x 13 baking dish.
Sprinkle the mini marshmallows evenly over the top in a single layer. (Don't overload the marshmallows.
Bake at 350 degrees F for about 30 minutes or just until the marshmallows are golden brown.
To learn how to "bake" sweet potatoes in an Instant Pot, check out my Instant Pot Sweet Potatoes recipe. Then you can mash the sweet potatoes and use them in this recipe.To Make Optional Pecan Streusel Topping.
In a bowl, stir together 1/4 cup (1/2 stick) softened butter, and 1/2 cup each: brown sugar, flour, and pecans.
Sprinkle over the top of the sweet potatoes and marshmallows.