- Boil yams until not quite fork tender. Remove from water and let cool. Remove skins and slice yams lengthwise into quarter pieces. Set aside.
- Cut butter into small cubes.
- In a 9x13 baking dish spoon about 1/4 of the pineapple, 1/4 of the butter cubes, and 1/4 of the brown sugar in the bottom of the dish. Lay the slices of yams over the top. Put the rest of the butter between slices. Pour the remaining of the pineapple over the top and sprinkle the remaining brown sugar over the top. Bake at 400 degrees for approximately 30 minute Sprinkle marshmellows over the top and make an additional 10-15min. Serve hot.