Preheat oven to 350 degrees. Butter a shallow baking dish or casserole (9x13 pan)
Prepare and boil whole yams or sweet potatoes until soft but not falling apart. Drain, set aside to cool. Once cooled, peel and cut into 1/4 inch slices.
Arrange slices, overlapping, in a buttered, shallow, baking dish or casserole
Dot with butter, sprinkle lightly with salt, cinnamon and nutmeg. Drizzle with orange juice or rum.
Bake uncovered for 30 minutes or until bubbly or glazed looking
Remove from oven and scatter the marshmallows over the top.
Bake again until the marshmallows are warmed through and start to brown.