Maple-Glazed Sweet Potatoes

Ingredients:

• 4 tablespoons vegetable oil, divided
• 4 pounds red-skinned sweet potatoes (yams), peeled, cut into 3/4-inch chunks
• 1/2 cup pure maple syrup (preferably grade b)
• 3 tablespoons unsalted butter, cut into 1/2-inch cubes

Source