Arrange oven rack in middle position and heat to 325º.

In a large pot over high heat, boil sweet potatoes, until nearly cooked through, about 20 minutes. Drain.

When cool enough to handle, peel and arrange potatoes in a single layer in a 13x9-inch baking pan.

In a medium-size saucepan over medium-high heat, bring maple syrup, butter, salt, and cider to a boil.

Pour over potatoes and bake in slow oven 1 hour, or until potatoes are glazed and syrup is of desired consistency.