- Heat 12-inch Dutch oven over about 9 coals.
- Arrange 4 jar rings evenly spaced on the bottom.
- Place each whole, pierced yam on top of the canning jar rings. Cover with Dutch oven lid and place about 15 hot coals on top. Cook covered for 30 minutes, turning yams over once.
- Cut yams in half lengthwise, fluff the center with a fork and add margarine, brown sugar and cinnamon.
- Cook, covered, 10 to 15 minutes more, if needed.