In a 6 quart dutch oven, combine sweet potatoes, heavy cream, butter, sugar and salt. Cover and cook over medium heat, stirring occasionally for about 20 minutes, or until sweet potatoes start to soften.

Preheat oven to 425 degrees. Reduce heat to medium low and continue cooking uncovered for about 20 minutes until potatoes are completely tender. 

Do not drain potatoes, add cream cheese and mash until smooth. Stir in toasted pecans. 

Spray a 2 quart baking dish with non stick cooking spray. Transfer sweet potatoes to baking dish and top with marshmallows. Place in oven and let marshmallows toast for about 5 minutes, watching closely to prevent burning.