Drain the yams until a little moisture is left.Mash yams in a medium bowl with your hands. Roll them around a marshmallow. [They should be about the size of a lime.] Crunch up corn flakes and roll the balls in the bag. Set yam balls in an ungreased round or rectangle pan. Cook on 350 degrees for 25-30 minutes. Remove from oven. Pour butter over. Sprinkle with brown sugar. Let cool for a few minutes before serving. Do not worry if they are not all in one piece when finished. Enjoy! This is a traditional dish from Basque, Spain.