Position racks in the top and bottom thirds of the oven and heat the oven to 425 degrees F. Put two large rimmed baking sheets in the hot oven. In a large bowl, toss the potatoes, olive oil, 1-1/2 teaspoons salt, and several grinds of pepper. When the pans are hot, divide the potatoes between the pans in a snug single layer (they should sizzle). Roast for 20 minutes, stirring occasionally, and then rotate the pans. Continue to roast, stirring occasionally, until they are browned in spots and tender when pierced with a fork, about 40 minutes longer. Return the potatoes to the large bowl, add the chives and truffle oil, if using, and toss. Season to taste with more salt and pepper and pour onto a serving platter (make sure to pour all the oil in the bowl over the potatoes). Keep warm until ready to serve.