Preparation

• Light a charcoal or gas fire. Combine all the ingredients in a bowl and mix well. Meanwhile, measure out three 20-inch-long sheets of 12-inch-wide foil and overlap two of them in a cross pattern. Mound the potato mixture in the middle of the cross and spread it out into a square that’s about 1-1/2 inches deep all around. Fold the ends of the foil in and wrap the package tightly. Wrap the third piece of foil around the package to seal.
• When the grill is medium hot, put the package on the grate directly over the hottest part. Cover the grill, making sure that the top and bottom vents are open (if using a charcoal grill). Cook for 20 minutes. Using tongs, turn the package over and cook for another 20 minutes. If your fire is very hot, shorten the cooking times by a couple of minutes on both sides. If it’s cooler, lengthen the total cooking time to 45 to 50 minutes.
• Open the package carefully with tongs; the steam will be very hot. The potatoes are done when they feel tender when pierced and some are deep brown and charred. Kept wrapped, they’ll stay warm off the grill for 15 to 20 minutes.

Add cooked bacon, diced ham, or lemon slices to the packets. Try replacing the garlic with shallots, or use sage instead of rosemary.