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Bake or microwave 8 medium yams. Once they're cool enough to handle peel them and slice them in half lengthwise. Or if you're roasting the yams, you can peel and slice them before you bake them. Lay the cooked yams in a 9 x 13-inch (22 x 33-cm) baking dish in a single layer. Measure 2 12 cups (590 ml) of water into a 2-quart (1.9-liter) saucepan. Stir in 1 13 cups (266 g) of packed dark brown sugar, 4 tablespoons (56 g) of butter, 1 12 teaspoons (4 g) of cinnamon, and 1 12 teaspoons (7 ml) of vanilla. Turn the oven on to 400 degrees F (200 degrees C). Turn the heat to high so the syrup ingredients come to a boil. Turn the heat down to medium-low so the mixture bubbles gently. Simmer the syrup for about 45 minutes so it begins to thicken and reduce. You'll need to stir the syrup every once in a while to prevent it from sticking. Carefully pour the syrup over the cooked yams in the baking dish. Ensure that all of the yams are coated with the syrup. If you want to use mini-marshmallows, sprinkle 1 1/2 cups (75 g) of mini-marshmallows over the yams. Place the yams in the preheated oven and bake them for about 45 minutes. The yams will soften even more and the syrup will look bubbly. Let the candied yams sit for a few minutes before you serve them. To help the yams cook evenly, you might want to spoon some of the syrup over them every 15 minutes during the cooking time.

Summary:
Cook 8 medium yams and slice them. Combine the syrup ingredients and preheat the oven. Cook the syrup for about 45 minutes. Pour the syrup over the yams and cover with the mini-marshmallows. Bake the candied yams for 45 minutes. Finished.