Scrub and boil in salted water whole sweet potatoes until just tender (25-40 minutes). Preheat oven to 375. Drain, peel, and cut potatoes into 1/2" slices. In 1 1/2-quart casserole layer half each of the potatoes, brown sugar, butter and salt. Repeat layers. Bake uncovered for 30-40 minutes or until glazed. Sprinkle marshmallows over top. Bake about 5 minutes more until lighltly browned.
