These potatoes are grilled to tender perfection in an aluminum foil pouch.
Preheat a grill until medium hot. If necessary, cut potatoes to uniform size to ensure even cooking. In a large bowl, combine potatoes, olive oil, salt, pepper, rosemary, and garlic. Toss to combine.
Place potatoes on one half of a 12-by-24-inch piece of heavy-duty aluminum foil. Fold foil over potatoes, and seal, forming a package.
Place package on the grill. Grill potatoes until fork-tender, 35 to 45 minutes. Serve.