Toss sweet potatoes with oil on a rimmed baking sheet. Season with salt and pepper. Bake 25 minutes, stirring halfway through cooking time.
While potatoes are roasting, heat apple cider in a small saucepan over high heat. Bring to a boil and cook until reduced to about 2 tablespoons, about 12 minutes.
Drizzle sweet potatoes with apple cider reduction; toss to coat. Bake 5 minutes more.
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