Place sweet potato cubes in a large saucepan, just cover with water and boil on stove top for 12 minutes or until soft
Drain all water and mash sweet potato. Add butter and sour cream and whip with a wooden spoon until you get a nice consistency
Spread sweet potato mash into a low baking tray and place white marshmallows on top *this recipe can also be made using So Soft Jumbo Marshmallows cut in half*
Sprinkle walnuts over the marshmallows and bake in oven at 170 degrees for approximately 10 minutes or until marshmallow tops are well toasted
Serve immediately
*Note: This recipe is absolutely delicious served as a side accompaniment to steak or chicken