Preheat the oven to 400°. Arrange the potatoes in a roasting pan and toss with the olive oil. Season with salt and nestle the rosemary sprigs into the potatoes. Roast for 30 minutes, then flip the potatoes; they should be golden brown. If they stick, don't loosen them. After they cook a few minutes more, you'll be able to flip them over. Roast for another 15 minutes and serve.