1. Heat a charcoal grill until coals form white ash, or preheat a gas grill. Spray a large piece of heavy-duty foil generously with cooking spray.

2. Arrange the onion slices in center of the foil. Place potatoes, cut sides up, on the onion slices. Drizzle the butter over potatoes and sprinkle with the salt, pepper, garlic salt and rosemary. Fold foil to enclose vegetables; seal tightly. 

3. Grill for 40 minutes, turning once. Open foil and fold back edges. Grill for 5 minutes longer or until the potatoes are tender.


Time Saver
In a hurry? Microwave the potato halves on HIGH for 1 1/2 to 2 minutes before adding to the onion. This will reduce the grilling time to just 20 minutes.