Truly Candied Yams (Sweet Potatoes)

In a 9- by 13-inch baking dish, arrange sweet potato rounds in an even layer, overlapping where necessary to fit them all. Set aside.

In a small saucepan, combine brown sugar, butter, water, and salt and bring to a boil, stirring often, until syrup registers 223°F (106°C) on an instant-read thermometer, about 8 minutes. Stir in cider vinegar, cinnamon, allspice, and ginger, then pour syrup all over sweet potatoes, spooning it over them as necessary to wet them completely.

Cover baking dish with aluminum foil and place in a cold oven. Turn on oven to 325°F (160°C) and allow it to come up to temperature. Cook, stopping to flip and baste sweet potatoes with syrup every 20 minutes, until tender throughout, about 40 minutes. (Exact cooking time will depend on your oven, baking dish, and the size of your sweet potatoes, so check frequently.)

Remove foil and continue to cook, flipping and basting sweet potatoes occasionally, until they are very soft and glazed in a rich brown syrup, about 20 minutes longer. Let cool slightly, then serve.