Thanksgiving-Marshmallow or Streusel Sweet Potatoes

6 large sweet potatoes
1/2 cup butter (smart balance)
3/4 cup brown sugar (was 2 cups white sugar)
1/2 teaspoon ground cinnamon (was 1 tsp)
1/2 teaspoon ground nutmeg (was 1 tsp)
1/2 tablespoon vanilla extract (was 1 tbsp)
salt to taste
about 2 cups miniature marshmallows
OR
Pecan Streusel Topping:
1 cup light brown sugar
1/2 cup featherlight GF mix (1 part each cornstarch, tapioca flour, and rice flour, +1/16 part potato starch flour: 1 tbsp if 1 part=1 cup)
1/3 cup butter (shortening)
1 cup chopped pecans

Peel sweet potatoes, cut in half length-wise, then into 2-inch segments. Boil for 15 minutes, or until still firm. Drain and return to pan. While they are cooking, combine remaining ingredients in a saucepan until butter is melted. Pour sauce into sweet potatoes. Stir, mashing half and leaving the rest as bite-size chunks. Pour into a 9x13. Top with Pecan Streusel if desired. Bake for 15 minutes at 400 F. If using marshmallows instead, top with marshmallows at this point and return to oven until marshmallows are toasted, about 3 minutes.