Cost per Serving:
1. Preheat oven to 400°F. Place potatoes on a baking sheet. Drizzle with oil and sprinkle with salt and pepper. Toss to coat. Spread potatoes in a single layer; prick each one several times with a paring knife. Roast until fork-tender, about 45 minutes. Let stand until just cool enough to handle.
2. Use a paring knife to split potatoes; don't cut all the way through. Push sides in so potatoes open up. Sprinkle each with Gruyère. Place back in oven and bake until cheese melts, about 5 minutes. Let cool until warm, then top with sour cream and chives. Season with salt and pepper; serve.