In a pot: bring the water to a boil. Add chopped sweet potatoes. Cook for 20-25 minutes or until tender. Drain the potatoes.
Preheat the oven to 375°F (190°C).
In a large bowl, combine cooked potatoes, heavy cream, brown sugar, vanilla extract, cinnamon, salt, butter and eggs together; mix well.
Spray cooking olive oil or butter to the baking pan. Transfer the sweet potato mixture to the pan.
Spread 2 cups of miniature marshmallows on top of the sweet potato mixture.
Bake (uncovered) for 25 minutes or until marshmallow are golden brown (keep a eye on the marshmallows, you don't want to burn them).
Note: This can be prepared a day or so ahead, do not bake, then cover and refrigerate. When ready to bake: let the dish sit at room temperature for ~1 hour and top with marshmallows and cook as directed above.