Step 1

Preheat oven to 400°F. Oil 2 large rimmed baking sheets with 1 tablespoon oil each. Combine sweet potatoes and remaining 2 tablespoons oil in large bowl; toss. Divide sweet potatoes between baking sheets, spreading evenly. Sprinkle with salt and pepper. Roast until almost tender, turning occasionally with metal spatula, about 35 minutes. DO AHEAD Can be prepared 2 hours ahead. Let stand uncovered at room temperature.

Step 2

Drizzle maple syrup over sweet potatoes and toss to coat. Roast until sweet potatoes are tender and syrup is reduced to 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 amount of cracked pepper.