Cook sweet potatoes in their jackets in a pot of boiling water until fork-tender. Drain and allow to cool for about 5 minutes for easy handling.
Peal and mash well or whip lightly with a bater. Add salt and butter to taste. Add the chopped nuts and mix well.
Lightly spoon the mixture into a buttered casserole and bake in moderately hot oven until well heated through. Remove from the oven and quickly top with miniature marshmallows for a decorative touch and return to the oven until marshmallows are delicately browned.