Preparation / Directions:
Prepare grill or heat oven to 450 degrees. Make a try using heavy duty aluminum foil. Cut potatoes into pieces no larger than 1-1/2 inches. Combine the potatoes, garlic, 1 tbsp oil and 1/4 tsp salt in a medium sized bowl. Toss to coat potatoes. Spoon potato mixture into the foil tray, keeping them in a single layer. Top with rosemary sprigs. Grill the potatoes for 25-30 minutes, turning occasionally, until tender and crisply browned OR roast in a baking pan at 450 degrees, stirring occasionally, until tender and browned (30 to 40 minutes). Meanwhile whisk vinegar, mustard, remaining 1/4 tsp salt and pepper. Whisk in remaining 3 tbsp oil. Discard woody rosemary stems from the potatoes. Squeeze garlic cloves from the skins into the dressing, and mash slightly in the dressing. Add potatoes and onions to the dressing, tossing to coat. Serve warm.