Dont wait until the holidays to serve these potatoes. These are great with roast chicken, pork or salmon.
Preheat oven to 400F. Oil 2 large rimmed baking sheets with 1 tablespoon each. Combine sweet potatoes and remaining 2 tablespoons oil in a large bowl; toss. Divide potatoes between baking sheets, spreading evenly. Sprinkle with salt and pepper. Roast until almost tender, turning occasionally with metal spatula, about 35 minutes. (Can be prepared 2 hours ahead. Let stand uncovered at room temperature.)
Drizzle maple syrup over sweet potatoes and toss to coat. Roast until sweet potatoes are tender and syrup is reduced to a glaze and coats sweet potatoes, about 20 minutes. Remove from oven; scatter butter cubes over sweet potatoes and let stand until melted. Season to taste with salt and generous amounts of cracked pepper.