Place yams in large baking dish. Bake in preheated oven for 15 minutes.
Meanwhile, in medium saucepan, combine corn syrup, sugar, half-and-half, butter, salt, and cinnamon. Stirring constantly, bring to a boil, and boil for 5 minutes. Pour over yams.
Bake, basting often, 15 minutes more.
(If you have to have marshmallows on your yams, sprinkle mini marshmallows over finished yams, and broil for 3 minutes or so, until melted and nicely browned.).