Place the diced potatoes in a bowl. Add the minced rosemary and garlic along with the oil and salt, and toss with your hands, coating the potatoes well.
Oil a roasting pan and spread the potatoes evenly over the bottom. Heat the oil to 425 degrees F.
Bake until the potatoes are crisp and golden brown, about 45 minutes, turning them every 10-15 minutes with a spatula and spreading them out in a single layer.
